Flexible Display Device with Chamfered Polarization Layer

ABSTRACT

There is provided a flexible display having a plurality of innovations configured to allow bending of a portion or portions to reduce apparent border size and/or utilize the side surface of an assembled flexible display.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 15/017,542 filed on Feb. 5, 2016, which is acontinuation application of U.S. patent application Ser. No. 14/586,387filed on Dec. 30, 2014, which are incorporated by reference herein intheir entirety.

BACKGROUND Technical Field

This relates generally to electronic devices, and more particularly, toelectronic devices with a display.

Description of the Related Art

Electronic devices often include displays. For example, cellulartelephones and portable computers include displays for presentinginformation to a user. Components for the electronic device, includingbut not limited to a display, may be mounted in a plastic or a metalhousing.

An assembled display may include a display panel and a number ofcomponents for providing a variety of functionalities. For instance, oneor more display driving circuits for controlling the display panel maybe included in a display assembly. Examples of the driving circuitsinclude gate drivers, emission (source) drivers, power (VDD) routing,electrostatic discharge (ESD) circuits, multiplex (mux) circuits, datasignal lines, cathode contacts, and other functional elements. There maybe a number of peripheral circuits included in the display assembly forproviding various kinds of extra functions, such as touch sense orfingerprint identification functionalities. Some of the components maybe disposed on the display panel itself, often in the periphery areasnext to the display area, which is referred in the present disclosure asthe non-display area and/or the inactive area.

Size and weight are of the critical importance in designing modernelectronic devices. Also, a high ratio of the active area size comparedto that of inactive area, which is sometimes referred to as the screento bezel ratio, is one of the most desired feature. However, placingsome of the aforementioned components in a display assembly may requirelarge inactive area, which may add up to a significant portion of thedisplay panel. Large inactive area tends to make the display panelbulky, making it difficult to incorporate it into the housing ofelectronic devices. Large inactive area may also necessitate a largemasking (e.g., bezel, borders, covering material) to cover a significantportion of the display panel, leading to unappealing device aesthetics.

Some of the components can be placed on a separate flexible printedcircuit (FPC) and positioned on the rear side of the display panel. Evenwith such a configuration, however, the interfaces for connecting theFPC and the wires between the active area and the connection interfacestill limit how much reduction in the size of the inactive area can berealized by placing components on a separate FPC.

BRIEF SUMMARY

Accordingly, it is desirable to bend the base substrate where thedisplay area and the inactive area are formed thereon. This would alloweven some of the inactive area to be positioned behind the active areaof the display panel, thereby reducing or eliminating the inactive areathat needs to be hidden under the masking or the device housing. Notonly does the bending of the base substrate will minimize the inactivearea size need to be hidden from view, but it will also open possibilityto various new display device designs.

However, there are various new challenges that need to be solved inproviding such flexible displays. The components formed directly on thebase substrate along with the display pixels tend to have tremendouslysmall dimensions with unforgiving margin of errors. Further, thesecomponents need to be formed on extremely thin sheet to provideflexibility, making those components extremely fragile to variousmechanical and environmental stresses instigated during the manufactureand/or in the use of the displays. If care is not taken, the mechanicalstresses from bending of the flexible display can negatively affect thereliability or even result in complete component failure. Even amicro-scale defect in the component thereof can have significant effectson the performance and/or reliability of the display pixels amounting toscrap the entire display panel without an option to repair. As such,various factors and special parameters must be taken in consideration indesigning a flexible display.

In this regards, a flexible display apparatus is provided with aflexible base layer. The flexible base layer is defined with a firstarea, a second area and a first bend allowance section, which ispositioned between the first area and the second area of the flexiblebase layer. The bend allowance section between the first area and thesecond area is curved in a certain bend angle so that the plane of thesecond area with the driving circuit is bent away from the plane of thefirst area. An active area, which includes an array of organic-lightemitting diode (OLED) elements is provided in at least one of the firstarea and the second area of the flexible base layer. An array of pixelcircuits is also provided in the active area to control emission of theOLED elements. A driving circuit is provided in an inactive area, whichis at the periphery of the active area. The driving circuit in theinactive area is configured to transmit various signals to the array ofpixel circuits in the active area. The inactive area may be provided inat least one of the first area and the second area of the flexible baselayer. In the active area, a polarization layer with a configuration(e.g., a shape, a size, a position and an orientation) such that thepolarization layer is unaffected by trimming of the flexible base layer.The trimming of the base layer may be achieved by at least one ofscribing, chamfering, cutting and grinding the flexible base layer intoa predetermined shape.

In one embodiment, the polarization layer is configured not to crossover a processing line related to the trimming of the flexible baselayer. When laser chamfering is used to trim the base layer, thepolarization layer is configured not to cross over the chamfer line.

In one embodiment, the polarization layer has a trimmed corner. Thetrimmed corner of the polarization layer may be trimmed in substantiallythe same angle as the processing line related to the trimming of theflexible base layer. In other words, the trimmed corner of thepolarization layer may be chamfered in the same direction as thechamfered corner of the base layer. In another, the base layer includesa notch, and the trimmed corner of the polarization layer corresponds tothe shape of the processing line at the notch of the flexible baselayer. That is, the polarization layer's corner toward the notch istrimmed in the same shape as the notch of the base layer. In yet anotherembodiment, the polarization layer has a rounded corner.

In some embodiments, the first area of the flexible base layer isprovided in a rounded shape, which can be placed within a roundedhousing. The second area or the third area of the flexible base layermay be protruded out from the first area of the flexible base layer. Thesecond area or the third area may be in a rectangular shape or any othershape sufficient to hold some components of the flexible display, suchas a display driver integrated circuit, gate-in-panel circuit, wiretraces, etc. Accordingly, the flexible base layer may have the roundshaped first area with a rectangular second area or a third areaextended out from the shape of the first area. The bend allowancesection between the first area and the second/third area(s) allow thesecond/third area(s) to be placed under the plane of the first area.This would allow the flexible base layer to be fit in to the roundshaped housing, and provide a device with a rounded display. In someembodiments, a notch may be provided in the bend allowance sectionbetween the first area and the second area to reduce the size of bendallowance section, which would be the edge of the flexible display afterthe bending of the flexible base layer. In some embodiments, a notch maybe provided in the bend allowance section between the first area and thethird area to reduce the size of bend allowance section. The notchprovided in the bend allowance section would also facilitate easierbending of the flexible base layer.

In another aspect, a flexible display is provided with a flexible baselayer that is chamfered in a predetermined shape. An array of organiclight-emitting diode (OLED) elements is provided on the flexible baselayer. The flexible display further includes an upper layer provided onthe array of OLED element, which is chamfered separately from theflexible base layer. The chamfered upper layer may be at least one of apolarization layer, a barrier film layer, a touch sensor layer, anadhesive layer and an optical sheet layer. The chamfered upper layer hasa shape and a size corresponding to those of the chamfered flexible baselayer, so that the chamfered upper layer on the array of OLED elementprovides clearance of a chamfer line of the chamfered flexible baselayer. This minimizes damage in one or more insulation layers interposedbetween the chamfered upper layer and the chamfered flexible base layer.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the embodiments discussed herein. A furtherunderstanding of the nature and advantages of certain embodiments may berealized by reference to the remaining portions of the specification andthe drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematic view of an exemplary flexible displayapparatus according to embodiments of the present disclosure.

FIG. 2 illustrates exemplary arrangement of a substantially flat portionand bend portion of a flexible display apparatus according toembodiments of the present disclosure.

FIGS. 3A and 3B illustrate exemplary arrangement of active areas of aflexible display apparatus according to embodiments of the presentdisclosure.

FIG. 4 illustrates simplified stack-up structure of components in anexemplary flexible display apparatus according to embodiment of thepresent disclosure.

FIG. 5 illustrates various examples of bend patterns applicable tofacilitate bending of a display apparatus.

FIGS. 6A-6D are cross-sectional views of illustrative arrangement ofcomponents in a flexible display apparatus according to variousembodiments of the present disclosure.

FIGS. 7A and 7B illustrate schematic view of an exemplary multi-layeredconductive lines and insulation layers according to embodiments of thepresent disclosure.

FIG. 8A illustrates exemplary arrangement of bridged conductive lines ina non-display area with a bend allowance section according toembodiments of the present disclosure.

FIG. 8B illustrates exemplary arrangement of bridged conductive lines ina non-display area without a bend allowance section according toembodiments of the present disclosure.

FIG. 9A illustrates a cross-sectional view of an exemplary configurationof bridged conductive lines according to embodiments of the presentdisclosure.

FIG. 9B illustrates a cross-sectional view of an exemplary configurationof bridged conductive lines according to embodiments of the presentdisclosure.

FIG. 10 illustrates schematic view of exemplary non-splitstrain-reducing trace designs usable for wire traces in a flexibledisplay apparatus according to embodiments of the present disclosure.

FIGS. 11A and 11B illustrate a schematic view of exemplarystrain-reducing wire trace designs having a plurality of sub-traces thatsplit and merge at a certain interval according to embodiments of thepresent disclosure.

FIG. 12 illustrates an exemplary arrangement of the wire tracesincluding indented sections and distended sections.

FIGS. 13A and 13B illustrate schematic cross-sectional views ofexemplary trace designs usable for wire traces in a flexible displayapparatus according to embodiments of the present disclosure.

FIGS. 14A and 14B illustrate schematic views of an exemplarystrain-reducing wire trace design with modified portions adopted for thewire trace to extend across the areas with different plane levels withinthe flexible display according to embodiments of the present disclosure.

FIG. 15A is a schematic cross-sectional view of an embodiment of aflexible display cut along the line A-A′ of FIG. 1.

FIG. 15B is a schematic cross-sectional view of an embodiment of aflexible display cut along the line A-A′ of FIG. 1.

FIG. 16A illustrates a schematic view of an exemplary configuration forthe crack stopper structures according to an embodiment of the presentdisclosure.

FIGS. 16B and 16C illustrate schematic views of exemplary configurationsnear the notched area of the flexible display apparatus.

FIG. 16D is an enlarged view near the notched area of the flexibledisplay provided with another type of crack stopper structure accordingto an embodiment of the present disclosure.

FIGS. 17A-17C illustrate schematic views of the flexible displayprovided with a micro-coating layer according to embodiments of thepresent disclosure.

FIGS. 18A and 18B illustrate schematic views of embodiments of theflexible display in a bent state, which are provided with amicro-coating layer according to embodiments of the present disclosure.

FIGS. 19A and 19B illustrate schematic views of embodiments of theflexible display in a bent state, which are provided with multiple typesof micro-coating layers in the bend allowance section according toembodiments of the present disclosure.

FIGS. 20A and 20B illustrate schematic views of embodiments of theflexible display, which are provided with several regions between theencapsulation and the printed circuit (e.g., COF) provided withdifferent types of micro-coating layers according to embodiments of thepresent disclosure.

FIG. 21 illustrates a schematic view of an exemplary strain-reducingwire trace design provided with elongated channel(s) for improvingspread dynamics of a micro-coating layer.

FIG. 22 illustrates a schematic view of an exemplary arrangement of aprinted circuit and a base layer in an embodiment of the flexibledisplay.

FIGS. 23A-23D are plan views illustrating exemplary configurations ofthe connectors on the first printed circuit in the FOP area.

DETAILED DESCRIPTION Flexible Display

FIG. 1 illustrates exemplary flexible display 100 which may beincorporated in electronic devices. Referring to FIG. 1, the flexibledisplay 100 includes at least one active area (i.e., display area), inwhich an array of display pixels are formed therein. One or moreinactive areas may be provided at the periphery of the active area. Thatis, the inactive area may be adjacent to one or more sides of the activearea. In FIG. 1, the inactive area surrounds a rectangular shape activearea. However, it should be appreciated that the shapes of the activearea and the arrangement of the inactive area adjacent to the activearea are not particularly limited as the exemplary flexible display 100illustrated in FIG. 1. The active area and the inactive area may be inany shape suitable to the design of the electronic device employing theflexible display 100. Non-limiting examples of the active area shapes inthe flexible display 100 include a pentagonal shape, a hexagonal shape,a circular shape, an oval shape, and more.

Each pixel in the active area may be associated with a pixel circuit,which includes at least one switching thin-film transistor (TFT) and atleast one driving TFT on the backplane of the flexible display 100. Eachpixel circuit may be electrically connected to a gate line and a dataline to communicate with one or more driving circuits, such as a gatedriver and a data driver positioned in the inactive area of the flexibledisplay 100.

For example, one or more driving circuits may be implemented with TFTsfabricated in the inactive area as depicted in FIG. 1. Such a drivingcircuit may be referred to as a gate-in-panel (GIP). Also, some of thecomponents, such as data drive-IC, may be mounted on a separate printedcircuit and coupled to a connection interface (Pads/Bumps, Pins)disposed in the inactive area using a printed circuit such as flexibleprinted circuit board (PCB), chip-on-film (COF), tape-carrier-package(TCP) or any other suitable technologies. As will be described infurther detail below, the inactive area with the connection interfacecan be bent away from the plane of the adjacent portion of the flexibledisplay so that the printed circuit (e.g., COF, PCB and the like) ispositioned at the rear side of the flexible display 100.

The flexible display 100 may include various additional components forgenerating a variety of signals or otherwise operating the pixels in theactive area. Non limiting examples of the components for operating thepixels include an inverter circuit, a multiplexer, an electro staticdischarge (ESD) circuit and the like. The flexible display 100 may alsoinclude components associated with functionalities other than foroperating the pixels of the flexible display 100. For instance, theflexible display 100 may include components for providing a touchsensing functionality, a user authentication functionality (e.g., fingerprint scan), a multi-level pressure sensing functionality, a tactilefeedback functionality and/or various other functionalities for theelectronic device employing the flexible display 100. Some of theaforementioned components can be placed in the inactive area of theflexible display 100 and/or on a separate printed circuit that isconnected to the connection interface of the flexible display 100.

Flat/Bend Portions

Multiple parts of the flexible display 100 can be bent along the bendline BL. The bend line BL in the flexible display 100 may extendhorizontally (e.g., X-axis shown in FIG. 1), vertically (e.g., Y-axisshown in FIG. 1) or even diagonally. Accordingly, the flexible display100 can be bent in any combination of horizontal, vertical and/ordiagonal directions based on the desired design of the flexible display100.

As mentioned, one or more edges of the flexible display 100 can be bentaway from the plane of the central portion along the bend line BL.Although the bend line BL is depicted as being located near the edges ofthe flexible display 100, it should be noted that the bend lines BL canextend across the central portion or extend diagonally at one or morecorners of the flexible display 100. Such configurations would allow theflexible display 100 to provide a foldable display or a double-sideddisplay having display pixels on both outer sides of a folded display.

With the ability to bend one or more portions of the flexible display100, part of the flexible display 100 may be defined as a substantiallyflat portion and a bend portion. A part of the flexible display 100 mayremain substantially flat and referred to as a substantially flatportion of the flexible display 100. A part of the flexible display 100may be bent in a certain bend angle from the plane of an adjacentportion, and such portion is referred to as a bend portion of theflexible display 100. The bend portion includes a bend allowancesection, which can be actively curved in a certain bend radius.

It should be understood that the term “substantially flat” includes aportion that may not be perfectly flat. For example, the concave centralportion and the convex central portion depicted in FIG. 2 may bedescribed as a substantially flat portion in some embodiments discussedin the present disclosure. In FIG. 2, one or more bend portions existnext to the convex or concave central portion, and bent inwardly oroutwardly along the bend line in a bend angle about a bend axis. Thebend radius of the bend portion is smaller than the bend radius of thecentral portion. In other words, the term “substantially flat portion”refers to a portion with a lesser curvature than that of an adjacentbend allowance section of the flexible display 100.

Depending on the location of the bend line BL in the flexible display100, a portion on one side of the bend line may be positioned toward thecenter of the flexible display 100, whereas the portion on the oppositeside of the bend line BL is positioned toward an edge portion of theflexible display 100. The portion toward the center may be referred toas the central portion and the portion toward the edge may be referredto as the edge portion of the flexible display 100. Although this maynot always be the case, a central portion of the flexible display 100can be the substantially flat portion and the edge portion can be thebend portion of the flexible display 100. It should be noted that asubstantially flat portion can also be provided in the edge portion ofthe flexible display 100. Further, in some configuration of the flexibledisplay 100, a bend allowance section may be positioned between twosubstantially flat portions.

As mentioned above, bending the inactive area allows to minimize or toeliminate the inactive area to be seen from the front side of theassembled flexible display 100. Part of the inactive area that remainsvisible from the front side can be covered with a bezel. The bezel maybe formed, for example, from a stand-alone bezel structure that ismounted to the cover layer 114, a housing or other suitable componentsof the flexible display 100. The inactive area remaining visible fromthe front side may also be hidden under an opaque masking layer, such asblack ink (e.g., a polymer filled with carbon black) or a layer ofopaque metal. Such an opaque masking layer may be provided on a portionof various layers included in the flexible display 100, such as a touchsensor layer, a polarization layer, a cover layer, and other suitablelayers.

Active Areas

In some embodiments, the bend portion of the flexible display 100 mayinclude an active area capable of displaying image from the bendportion, which is referred herein after as the secondary active area.That is, the bend line BL can be positioned in the active area so thatat least some display pixels of the active area is included in the bendportion of the flexible display 100.

FIGS. 3A and 3B each illustrates an exemplary configuration of activeareas in an embodiment of flexible display 100 of the presentdisclosure. In the configuration depicted in FIG. 3A, the matrix ofpixels in the secondary active area of the bend portion may becontinuously extended from the matrix of the pixels in the active areaof the central portion. Alternatively, in the configuration depicted inFIG. 3B, the secondary active area within the bend portion and theactive area within the central portion of the flexible display 100 maybe separated apart from each other by the bend allowance section of theflexible display 100. Some components in the central portion and thebend portion can be electrically connected via one or more conductiveline 120 laid across the bend allowance section of the flexible display100.

The pixels in the secondary active area and the pixels in the centralactive area may be addressed by the driving circuits (e.g., gate driver,data driver, etc.) as if they are in a single matrix. In this case, thepixels of the central active area and the pixels of the secondary activearea may be operated by the same set of driving circuits. By way ofexample, the N^(th) row pixels of the central active area and the N^(th)row pixels of the secondary active area may be configured to receive thegate signal from the same gate driver. As shown in FIG. 3B, the part ofthe gate line crossing over the bend allowance section (i.e., bendallowance region) or a bridge for connecting the gate lines of the twoactive areas may have a strain-reducing trace design, which will bedescribed in further detail below.

Depending on the functionality of the secondary active area, the pixelsof the secondary active area can be driven discretely from the pixels inthe central active area. That is, the pixels of the secondary activearea may be recognized by the display driving circuits as being anindependent matrix of pixels separate from the matrix of pixels of thecentral active area. In such cases, the pixels of the secondary activearea may receive signals from at least one discrete driving circuitother than a driving circuit for providing signals to the pixels of thecentral active area.

Regardless of the configuration, the secondary active area in the bendportion may serve as a secondary display area in the flexible display100. Also, the size of the secondary active area is not particularlylimited. The size of the secondary active area may depend on itsfunctionality within the electronic device. For instance, the secondaryactive area may be used to provide images and/or texts such a graphicaluser interface, buttons, text messages, and the like. In some cases, thesecondary active area may be used to provide light of various colors forvarious purposes (e.g., status indication light), and thus, the size ofthe secondary active area need not be as large as the active area in thecentral portion of the flexible display 100.

Stack-Up Structure

FIG. 4 is a simplified cross-sectional view showing an exemplary stackup structure of a flexible display 100 in an embodiment of the presentdisclosure. For convenience of explanation, the central portion of theflexible display 100 is illustrated as being substantially flat, and thebend portions are provided at the edges of the flexible display 100 inFIG. 4.

As shown, one or more bend portions may be bent away from the plane ofthe substantially flat portion in a certain bend angle θ and with a bendradius R about the bending axis. The size of each bend portion that isbent away from the central portion needs not be the same. That is, thelength of the base layer 106 from the bend line BL to the outer edge ofthe base layer 106 at each bend portion can be different from other bendportions. Also, the bend angle θ around the bend axis and the bendradius R from the bend axis can vary between the bend portions.

In the example shown in FIG. 4, the right side bend portion has the bendangle θ of 90°, and the bend portion includes a substantially flatsection. A bend portion can be bent at a larger bend angle θ, such thatat least some part of the bend portion comes underneath the plane of thecentral portion of the flexible display 100 as the bend portion on theleft side of the flexible display 100. Also, a bend portion can be bentat a bend angle θ that is less than 90°.

In some embodiments, the radius of curvatures (i.e., bend radius) forthe bend portions in the flexible display 100 may be between about 0.1mm to about 10 mm, more preferably between about 0.1 mm to about 5 mm,more preferably between about 0.1 mm to about 1 mm, more preferablybetween about 0.1 mm to about 0.5 mm. In some embodiments, the bendradius at a bend portion of the flexible display 100 may be less than0.5 mm.

One or more support layers 108 may be provided at the underside of thebase layer 106 to increase rigidity and/or ruggedness at the selectiveportion of the flexible display 100. For instance, the support layer 108can be provided on the inner surface of the base layer 106 at thesubstantially flat portions of the flexible display 100. The supportlayer 106 may not be provided in the bend allowance section where moreflexibility is needed. The support layer 106 may also be provided on thebase layer 106 of the bend portion that is positioned under the centralportion of the flexible display 100. Increased rigidity at selectiveparts of the flexible display 100 may help in ensuring accurateconfiguration and placement of various components during manufacturingand using the flexible display 100. The support layer 108 can also serveto suppress generation of cracks in the base layer 106, if the baselayer 106 has a higher modulus than the support layer 108.

The base layer 106 and the support layer 108 may each be made of a thinplastic film formed from polyimide, polyethylene naphthalate (PEN),polyethylene terephthalate (PET), other suitable polymers, a combinationof these polymers, etc. Other suitable materials that may be used toform the base layer 106 and the support layer 108 include, a thin glass,a metal foil covered with a dielectric material, a multi-layered polymerstack and a polymer composite film comprising a polymer materialcombined with nanoparticles or micro-particles dispersed therein, etc.Support layers 108 provided in various parts of the flexible display 100need not be made of the same material. For example, a thin-glass layermay be used as a support layer 108 for the central portion of theflexible display 100 while a thin plastic film layer is used as asupport layer 108 for edge portions.

In addition to the constituent material, the thickness of the base layer106 and the support layer 108 is another factors to consider indesigning the flexible display 100. On the one hand, bending of the baselayer 106 at a small bend radius can be difficult if the base layer 106has excessively high thickness. Also, excessive thickness of the baselayer 106 can increase mechanical stress to the components disposedthereon during bending the base layer 106. On the other hand, however,the base layer 106 can be too fragile to serve as a substrate forvarious components of the flexible display if it is too thin.

To meet such requirements, the base layer 106 may have a thickness in arange of about from 5 μm to about 50 μm, more preferably in a range ofabout 5 μm to about 30 μm, and more preferably in a range of about 5 μmto about 16 μm. The support layer 108 may have a thickness from about100 μm to about 125 μm, from about 50 μm to about 150 μm, from about 75μm to 200 μm, less than 150 μm, or more than 100 μm.

In one suitable exemplary configuration, a layer of polyimide with athickness of about 10 μm to about 16 μm serves as the base layer 106while a polyethylene terephthalate (PET) layer with a thickness of about50 μm to about 125 μm serves as the support layer 108. In anothersuitable exemplary configuration, a layer of polyimide with a thicknessof about 10 μm to about 16 μm serves as the base layer 106 while athin-glass layer with a thickness of about 50 μm to about 200 μm is usedas the support layer 108. In yet another suitable exemplaryconfiguration, a thin glass layer is used as the base layer 106 with alayer of polyimide serving as the support layer 108 to suppress breakingof the base layer 106.

During manufacturing, some part of the flexible display 100 may beexposed to external light. Some materials used in fabricating thecomponents on the base layer 106 or the components themselves mayundergo undesirable state changes (e.g., threshold voltage shift in theTFTs) due to the light exposure during the manufacturing of the flexibledisplay 100. Some parts of the flexible display 100 may be more heavilyexposed to the external light than others, and this can lead to adisplay non-uniformity (e.g., mura, shadow defects, etc.). To minimizesuch problems, the base layer 106 and/or the support layer 108 mayinclude one or more materials capable of reducing the amount of externallight passing through in some embodiments of the flexible display 100.

The light blocking material, for instance chloride modified carbonblack, may be mixed in the constituent material of the base layer 106(e.g., polyimide or other polymers). In this way, the base layer 106 mayformed of polyimide with a shade to provide a light blockingfunctionality. Such a shaded base layer 106 can also improve thevisibility of the image content displayed on the flexible display 100 byreducing the reflection of the external light coming in from the frontside of the flexible display 100.

Instead of the base layer 106, the support layer 108 may include a lightblocking material to reduce the amount of light coming in from the rearside (i.e., the support layer 108 attached side) of the flexible display100. The constituent material of the support layer 108 may be mixed withone or more light blocking materials in the similar fashion as describedabove with the base layer 106. Further, both the base layer 106 and thesupport layer 108 can include one or more light blocking materials.Here, the light blocking materials used in the base layer 106 and thesupport layer 108 need not be the same.

While making the base layer 106 and the support layer 108 to block theunwanted external light may improve display uniformity and reducereflection as described above, recognizing alignment marks for accuratepositioning of the components or for carrying out manufacturing processmay become difficult. For example, accurate positioning of thecomponents on the base layer 106 or the alignment during bending of theflexible display 100 can be difficult as the positioning of the layersmay need to be determined by comparing the outer edges of theoverlapping portions of the layer(s). Further, checking for unwanteddebris or other foreign materials in the flexible display 100 can beproblematic if the base layer 106 and/or the support layer 108 blocksthe excessive range(s) of light spectrum (i.e., wavelengths in thevisible, the ultraviolet and the infrared spectrum).

Accordingly, in some embodiments, the light blocking material, which maybe included in the base layer 106 and/or the support layer 108 isconfigured to pass the light of certain polarization and/or the lightwithin specific wavelength ranges usable in one or more manufacturingand/or testing processes of the flexible display 100. By way of example,the support layer 108 may pass the light to be used in quality checkand/or alignment processes (e.g., UV, IR spectrum light) during themanufacturing the flexible display 100, but filter the light in thevisible light wavelength range. The limited range of wavelengths canhelp reduce the display non-uniformity problem, which may be caused bythe shadows generated by the printed circuit attached to base layer 106,especially if the base layer 106 includes the light blocking material asdescribed above.

It should be noted that the base layer 106 and the support layer 108 canwork together in blocking and passing specific types of light. Forinstance, the support layer 108 can change the polarization of light,such that the light will not be passable through the base layer 106.This way, certain type of light can be passed through the support layer108 for various purposes during manufacturing of the flexible display100, but unable to penetrate through the base layer 106 to causeundesired effects to the components disposed on the opposite side of thebase layer 106.

Backplane of the flexible display 100 is implemented on the base layer106. In some embodiments, the backplane of the flexible display 100 canbe implemented with TFTs using low-temperature poly-silicon (LTPS)semiconductor layer as its active layer. In one suitable configuration,the pixel circuit and the driving circuits (e.g., GIP) on the base layer106 are implemented with NMOS LTPS TFTs. In other suitableconfiguration, the backplane of the flexible display 100 can beimplemented with a combination of NMOS LTPS TFTs and PMOS LTPS TFTs. Forinstance, the driving circuit (e.g., GIP) on the base layer 106 mayinclude one or more CMOS circuits to reduce the number of lines forcontrolling the scan signals on the gate line.

Further, in some embodiments, the flexible display 100 may employmultiple kinds of TFTs to implement the driving circuits in the inactivearea and/or the pixel circuits in the active area. That is, acombination of an oxide semiconductor TFT and an LTPS TFT may be used toimplement the backplane of the flexible display 100. In the backplane,the type of TFTs may be selected according to the operating conditionsand/or requirements of the TFTs within the corresponding circuit.

Low-temperature-poly-silicon (LTPS) TFTs generally exhibit excellentcarrier mobility even at a small profile, making them suitable forimplementing condensed driving circuits. The excellent carrier mobilityof the LTPS TFT makes it an ideal for components requiring a fast speedoperation. Despite the aforementioned advantages, initial thresholdvoltages may vary among the LTPS TFTs due to the grain boundary of thepoly-crystalized silicon semiconductor layer.

A TFT employing an oxide material based semiconductor layer, such as anindium-gallium-zinc-oxide (IGZO) semiconductor layer (referredhereinafter as “the oxide TFT”), is different from the LTPS TFT in manyrespects. Despite a lower mobility than the LTPS TFT, the oxide TFT isgenerally more advantageous than the LTPS TFT in terms of powerefficiency. Low leakage current of the oxide TFT during its off stateallows to remain in active state longer. This can be of a greatadvantage for driving the pixels at a reduced frame rate when a highframe rate driving of the pixels is not needed.

By way of example, the flexible display 100 may be provided with afeature in which the pixels of the entire active area or selectiveportion of the active area are driven at a reduced frame rate under aspecific condition. In this setting, the pixels can be refreshed at areduced refresh rate depending on the content displayed from theflexible display 100. Also, part of the active area displaying a stillimage data (e.g., user interface, text) may be refreshed at a lower ratethan other part of the active area displaying rapidly changing imagedata (e.g., movie). The pixels driven at a reduced refresh rate may havean increased blank period, in which the data signal is not provided tothe pixels. This would minimize the power wasted from providing thepixels with the same image data. In such embodiments, some of the TFTsimplementing the pixel circuits and/or the driving circuits of theflexible display 100 can be formed of the oxide TFT to minimize theleakage current during the blank period. By reducing the current leakagefrom the pixel circuits and/or the driving circuits, the pixels canachieve more stable level of luminance even when the display isrefreshed at a reduced rate.

Another feature of the oxide TFT is that it does not suffer from thetransistor-to-transistor initial threshold voltage variation issue asmuch as the LTPS TFTs. Such a property can be of a great advantage whenincreasing the size of the flexible display 100. Threshold shifts underbias stress is also different between LTPS TFT and oxide TFT.

Considering the aforementioned characteristics of LTPS TFT and oxideTFT, some embodiments of the flexible display 100 disclosed herein canemploy a combination of the LTPS TFT and the oxide TFT in a singlebackplane. In particular, some embodiments of the flexible display 100can employ LTPS TFTs to implement the driving circuits (e.g., GIP) inthe inactive area and employ oxide TFTs to implement the pixel circuitsin the active area. Due to the excellent carrier mobility of the LTPSTFTs, driving circuits implemented with LTPS TFTs may operate at afaster speed than the driving circuits implemented with the oxide TFTs.In addition, more condensed driving circuits can be provided with theLTPS TFT, which reduces the size of the inactive area in the flexibledisplay 100. With the excellent voltage holding ratio of the oxide TFTsused in the pixel circuits, leakage from the pixels can be reduced. Thisalso enables to refresh pixels in a selective portion of the active areaor to drive pixels at a reduced frame rate under a predeterminedcondition (e.g., when displaying still images) while minimizing displaydefects caused by the leakage current.

In some embodiments, the driving circuits in the inactive area of theflexible display 100 may be implemented with a combination of N-TypeLTPS TFTs and P-Type LTPS TFTs while the pixel circuits are implementedwith oxide TFTs. For instance, N-Type LTPS TFTs and P-Type LTPS TFTs canbe used to implement a CMOS gate driver (e.g., CMOS GIP, Data Driver)whereas oxide TFTs are employed in at least some part of the pixelcircuits. Unlike the GIP formed entirely of either the P-type or N-typeLTPS TFTs, the gate out signal from the CMOS gate driver can becontrolled by DC signals or logic high/low signals. This allows for morestable control of the gate line during the blank period such that thesuppression of current leakage from the pixel circuit or unintendedactivation of the pixels connected the gate line can be achieved.

It should be noted that a CMOS gate driver or an inverter circuit on thebackplane can be implemented by using a combination of LTPS TFTs andoxide TFTs. For instance, a P-type LTPS TFT and an N-Type oxide TFT canbe used to implement a CMOS circuit. Also, the pixel circuits in theactive area can also be implemented by using both the LTPS TFTs and theoxide TFTs. When employing both kinds of TFTs in the pixel circuitand/or the driving circuit, the LTPS TFT can be strategically placedwithin the circuit to remove bias remaining in a node between oxide TFTsduring their off state and minimize the bias stress (e.g., PBTS, NBTS).In addition, the TFTs in a circuit, which are connected to a storagecapacitor, can be formed of the oxide TFT to minimize leakage therefrom.

A layer of organic light-emitting diode (OLED) elements is disposed onthe base layer 106. The OLED element layer 102 includes a plurality ofOLED elements, which is controlled by the pixel circuits and the drivingcircuits implemented on the base layer 106 as well as any other drivingcircuits provided on a separate printed circuit, which is connected tothe connection interfaces on the base layer 106. The OLED element layerincludes an organic light-emitting material layer, which may emit lightof certain spectral color (e.g., red, green, blue). In some embodiments,the organic-light emitting material layer may have a stack configurationto emit white light, which is essentially a combination of multiplecolored lights.

The encapsulation 104 is provided to protect the OLED element layer 102from air and moisture. The encapsulation 104 may include multiple layersof materials for reducing permeation of air and moisture to protect OLEDelements thereunder. In some embodiments, the encapsulation 104 may beprovided in a form of a thin film.

The flexible display 100 may also include a polarization layer 110 forcontrolling the display characteristics (e.g., external lightreflection, color accuracy, luminance, etc.) of the flexible display100. Also, the cover layer 114 may be used to protect the flexibledisplay 100.

Electrodes for sensing touch input from a user may be formed on aninterior surface of a cover layer 114 and/or at least one surface of thepolarization layer 110. If desired, an independent layer with the touchsensor electrodes and/or other components associated with sensing oftouch input (referred hereinafter as touch-sensor layer 112) may beprovided in the flexible display 100. The touch sensor electrodes (e.g.,touch driving/sensing electrodes) may be formed from transparentconductive material such as indium tin oxide, carbon based materialslike graphene or carbon nanotube, a conductive polymer, a hybridmaterial made of mixture of various conductive and non-conductivematerials. Also, metal mesh (e.g., aluminum mesh, silver mesh, etc.) canalso be used as the touch sensor electrodes.

The touch sensor layer 112 may include a layer formed of one or moredeformable dielectric materials. One or more electrodes may beinterfaced with or positioned near the touch sensor layer 112, andloaded with one or more signals to facilitate measuring electricalchanges on one or more of the electrodes upon deformation of the touchsensor layer 112. The measurement may be analyzed to assess the amountof pressure at a plurality of discrete levels and/or ranges of levels onthe flexible display 100.

In some embodiments, the touch sensor electrodes can be utilized inidentifying the location of the user inputs as well as assessing thepressure of the user input. Identifying the location of touch input andmeasuring of the pressure of the touch input on the flexible display 100may be achieved by measuring changes in capacitance from the touchsensor electrodes on one side of the touch sensor layer 112. The touchsensor electrodes and/or other electrode may be used to measure a signalindicative of the pressure on the flexible display 100 by the touchinput. Such a signal may be obtained simultaneously with the touchsignal from the touch sensor electrodes or obtained at a differenttiming.

The deformable material included in the touch sensor layer 112 may be anelectro-active material, which the amplitude and/or the frequency of thedeformation is controlled by an electrical signal and/or electricalfield. The examples of such deformable materials include piezo ceramic,electro-active-polymer (EAP) and the like. Accordingly, the touch sensorelectrodes and/or separately provided electrode can activate thedeformable material to bend the flexible display 100 to desireddirections. In addition, such electro-active materials can be activatedto vibrate at desired frequencies, thereby providing tactile and/ortexture feedback on the flexible display 100. It should be appreciatedthat the flexible display 100 may employ a plurality of electro-activematerial layers so that bending and vibration of the flexible display100 can be provided simultaneously or at a different timing. Such acombination can be used in creating sound waves from the flexibledisplay 100.

Components of the flexible display 100 may make it difficult to bend theflexible display 100 along the bend line BL. Some of the elements, suchas the support layer 108, the touch sensor layer 112, the polarizationlayer 110 and the like, may add too much rigidity to the flexibledisplay 100. Also, the thickness of such elements shifts the neutralplane of the flexible display 100 and thus some of the components may besubject to greater bend stresses than other components.

To facilitate easier bending and to enhance the reliability of theflexible display 100, the configuration of components in the bendportion of the flexible display 100 differs from the substantially flatportion of the flexible display 100. Some of the components existing inthe substantially flat portion may not be disposed in the bend portionsof the flexible display 100, or may be provided in a differentthickness. The bend portion may be free of the support layer 108, thepolarization layer 110, the touch sensor layer 114, a color filter layerand/or other components that may hinder bending of the flexible display100. Such components may not be needed in the bend portion if the bendportion is to be hidden from the view or otherwise inaccessible to theusers of the flexible display 100.

Even if the secondary active area is in the bend portion for providinginformation to users, the secondary active area may not require some ofthese components depending on the usage and/or the type of informationprovided by the secondary active area. For example, the polarizationlayer 110 and/or color filter layer may not be needed in the bendportion when the secondary active area is used for simply emittingcolored light, displaying texts or simple graphical user interfaces in acontrast color combination (e.g., black colored texts or icons in whitebackground). Also, the bend portion of the flexible display 100 may befree of the touch sensor layer 114 if such functionality is not neededin the bend portion. If desired, the bend portion may be provided with atouch sensor layer 112 and/or the layer of electro-active material eventhough the secondary active area for displaying information is notprovided in the bend portion.

Since the bend allowance section is most heavily affected by the bendstress, various bend stress-reducing features are applied to thecomponents on the base layer 106 of the bend allowance section. To thisend, some of the elements in the central portion may be absent in atleast some part of the bend portion. The separation between thecomponents in the central portion and the bend portion may be created byselectively removing the elements at the bend allowance section of theflexible display 100 such that the bend allowance section is free of therespective elements.

As depicted in FIG. 4, the support layer 108 in the central portion andthe support layer 108 in the bend portion can be separated from eachother by the absence of the support layer 108 at the bend allowancesection. Instead of using the support layer 108 attached to the baselayer 106, a support member 116 with a rounded end portion can bepositioned underside of the base layer 106 at the bend allowancesection. Various other components, for example the polarization layer110 and the touch sensor layer 114 and more, may also be absent from thebend allowance section of the flexible display 100. The removal of theelements may be done by cutting, wet etching, dry etching, scribing andbreaking, or other suitable material removal methods. Rather thancutting or otherwise removing an element, separate pieces of the elementmay be formed at the selective portions (e.g., substantially flatportion and the bend portion) to keep the bend allowance section free ofsuch element.

Rather than being entirely removed from the bend portion, some elementsmay be provided with a bend pattern along the bend lines and/or theparts within the bend allowance section to reduce the bend stress. FIG.5 illustrates a plane view and a cross-sectional view of exemplary bendpatterns, which may be applied to some of the components. The bendpatterns described above may be used in the support layer 108, thepolarization layer 110, the touch sensor layer 112 and various otherelements of the flexible display 100.

The flexible display 100 may utilize more than one types of bendpatterns. It should be appreciated that a number of bend patterns andthe types of the bend patterns utilized by the components is notlimited. If desired, the depth of the patterns may not be deep enough topenetrate through the component entirely but penetrate only partiallythrough the respective layer. As will be described in further detailbelow, a buffer layer positioned between the base layer 106 and the TFTas well as a passivation layer covering a conductive line may be also beprovided with the bend pattern for reducing bend stress.

Support Member

As mentioned, the support layer 108 may not be present at the bendallowance section to facilitate easier bending of the base layer 106.Absent the support layer 108, however, the curvature at the bendallowance section may be easily altered by external force. To supportthe base layer 106 and maintain the curvature at the bend allowancesection, the flexible display 100 may also include a support member 116,which may also be referred to as a “mandrel.” The exemplary supportmember 116 depicted in FIG. 4 has an elongated body portion and arounded end portion. The base layer 106 and the support member 116 arearranged so that that the rounded end portion of the support member 116is positioned at the underside of the base layer 106 corresponding tothe bend allowance section of the flexible display 100.

In embodiments where a bend portion is provided at an edge of theflexible display 100, the support member 116 can be provided at the edgeof the flexible display 100. In this setting, a part of the base layer106 may come around the rounded end portion of the support member 116and be positioned at the underside the support member 116 as depicted inFIG. 4. Various circuits and components in the inactive area of theflexible display 100, such as drive ICs and connection interfaces forconnecting chip-on-flex (COF) and printed circuit board (PCB), may beprovided on the base layer 106 that is positioned at the rear side ofthe flexible display 100. In this way, even the components that are notflexible enough to be bent in a bend radius desired by the flexibledisplay 100 can be placed under the active area of the flexible display100.

The support member 116 can be formed of plastic material such aspolycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN),polyethylene terephthalate (PET), other suitable polymers, a combinationof these polymers, etc. The rigidity of the support member 116 formed ofsuch plastic materials may be controlled by the thickness of the supportmember 116 and/or by providing additives for increasing the rigidity.The support member 116 can be formed in a desired color (e.g., black,white, etc.). Further, the support member 116 may also be formed ofglass, ceramic, metal or other rigid materials or combinations ofaforementioned materials.

Size and shape of the rounded end portion of the support member 116 canvary depending on the minimum curvature desired at the bend allowancesection of the flexible display 100. In some embodiments, the thicknessof the rounded end portion and the thickness of the elongated bodyportion may be substantially the same. In other embodiments, theelongated body portion, which has a planar shape, may be thinner thanthe rounded end portion of the support member 116. With a thinnerprofile at the elongated body portion, the support member 116 cansupport the bend allowance section while avoiding unnecessary increasein the thickness in the flexible display 100.

Since the support at the bend allowance section is provided by therounded end portion of the support member 116, the elongated planarportion extending toward the substantially flat portion of the flexibledisplay 100 needs not be extended into the active area. While theelongated body portion can be extended under the active area for variousreasons, the length of the elongated body portion from the rounded endportion towards the opposite end is sufficient so long as it providesenough surface area for securing the support member 116 in a desiredlocation of the flexible display 100.

To secure the support member 116 in the flexible display 100, anadhesive layer 118 may be provided on the surface of the support member116. The adhesive layer 118 may include a pressure-sensitive adhesive, afoam-type adhesive, a liquid adhesive, a light-cured adhesive or anyother suitable adhesive material. In some embodiments, the adhesivelayer 118 can be formed of, or otherwise includes, a compressiblematerial and serve as a cushion for the parts bonded by the adhesivelayer 118. As an example, the constituent material of the adhesive layer118 may be compressible. The adhesive layer 118 may be formed ofmultiple layers, which includes a cushion layer (e.g., polyolefin foam)interposed between an upper and a lower layers of an adhesive material.

The adhesive layer 118 can be placed on at least one of the uppersurface and the lower surface of the elongated body portion of thesupport member 116. When the bend portion of the flexible display 100wraps around the rounded end portion of the support layer 116, anadhesive layer 118 can be provided on both the lower surface (i.e., thesurface facing the rear side) and the upper surface (i.e., the surfacefacing the front side) of the elongated body portion. If desired, anadhesive layer 118 may be provided between the surface of the roundedend portion of the support member 116 and the inner surface of the baselayer 106.

During bending, a part of the flexible display 100 on one side of thesupport member 116 may be pulled toward the support member 116, and thebase layer 106 may be damaged by the highest and the lowest edges of therounded end portion. As such, the height of the adhesive layer 118 andthe support layer 108 between the support member 116 and the base layer106 may be at least equal to or greater than the vertical distancebetween the highest edge of the rounded end portion and the surface ofthe elongate body portion where the adhesive layer 118 is placed. Inother words, the height of the space created by the thickness differencebetween the rounded end portion and the elongated body portion of thesupport member 116 may be equal to or less than the collective thicknessof the support layer 108 and the adhesive layer 118.

Depending on the shape of the support member 116, a thickness of theadhesive layer 118 on the upper and the lower surfaces of the elongatedbody portion may be different. For instance, the elongated body portion,which is thinner than the rounded end portion, may not be at the centerof the rounded end portion of the support member 116. In such cases, thespace on one side of the support member 116 may be greater than thespace on the opposite side.

In another example, the lowest edge of the rounded end portion may bein-line with the bottom surface of the elongated body portion such thatthe space is provided only on one side of the elongated body portion. Insuch cases, the adhesive layer 118 on one side of the elongated bodyportion of the support member 116 can be thicker than the one on theopposite side. It should be appreciated that the dimensions of thesupport member 116 in FIG. 4 may be exaggerated for the purposes ofsimpler explanation.

Exemplary Arrangement

FIGS. 6A, 6B, 6C and 6D are simplified cross-sectional views showingexemplary arrangements of elements in various embodiments of theflexible display 100. In one suitable configuration, which is depictedin FIG. 6A, the thickness of the rounded end portion and the elongatedbody portion of the support member 116A may be substantially the same asillustrated in FIG. 6A. Such a support member 116A can be formed of theplastic materials mentioned above. The support member 116A may also beformed of a folded thin sheet metal (e.g., SUS). In this case, thefolded edge of the sheet metal can serve as the rounded end portion ofthe support member 116A. Even when a sheet metal is used to form thesupport member, the rounded end portion can have greater thickness thanthe elongated body portion. For instance, pressure can be applied on thepart of the folded metal sheet for the elongated body portion to makethat portion thinner than the folded edge.

An adhesive layer 118A may be applied on the upper, the lower surfaceand the surface of the rounded end portion of the support member 116A.As the thickness of the support member 116A at the rounded end portionand the elongated body portion is about the same, the thickness of theadhesive layer 118A may have a substantially uniform thickness on thesurface of the support member 116A. However, it should be noted that theadhesive layer 118A can be thinner and/or thicker at selective parts ofthe support member 116A.

In another suitable configuration, which is depicted in FIG. 6B, theelongated body portion of the support member 116 is thinner than itsrounded end portion. In this regard, the bottom surface of the elongatedbody portion is in-line with the lowest edge of the rounded end portion,providing a support member 116B with a flat bottom. In this exemplaryconfiguration, the support members 116B may be formed of one or acombination of aforementioned plastic materials (e.g., polycarbonate).Also, the adhesive layer 118B provided on the upper surface of theelongated body portion is thicker than the adhesive layer 118B providedon the bottom surface of the elongated body portion of the supportmember 116B. The adhesive layer 118B on the upper surface of theelongated body portion may include a cushion layer described above whilethe adhesive layer 118B on the lower surface does not.

In yet another suitable configuration shown in FIG. 6C, neither the topnor the bottom surfaces of the elongated body portion of the supportmember 116C is in-line with the highest/lowest edges of the roundedportion. The support members 116C may be formed of one or a combinationof aforementioned plastic materials (e.g., polycarbonate). In thisexample, the elongated body portion may be off-centered (i.e., closer tothe lowest edge of the rounded portion), and the adhesive layer 118C onthe upper surface of the elongated body portion is thicker than theadhesive layer 118C on the lower surface. The adhesive layer 118C on theupper surface of the elongated body portion may include a cushion layerdescribed above while the adhesive layer 118C on the lower surface doesnot.

In the exemplary configurations depicted in FIGS. 6A-6C, the supportlayer 108 on the upper side of the support member 116 is extended outtoward the bend allowance section further than the encapsulation 104. Inother words, some of the support layer 108 near the edge of the flexibledisplay 100 is not overlapped by the encapsulation 104. The extra margin(denoted “A” in FIG. 6C) of the support layer 108 provided under theencapsulation 104 can help maintain a steady rate of curvature in thebend allowance section.

When bending the base layer 106 around the rounded end portion of thesupport member 116, the support layer 108 can be positioned on therounded end portion of the support member 116 due to alignment error. Insuch cases, the support layer 108 on the rounded end portion may pushaway the elements on the base layer 106 and shift the neutral plane orcause delamination of those elements in the bend portion of the flexibledisplay 100. As such, the support layer 108 under the base layer 106 isarranged such that the edge of the support layer 108 is extended outtoward the bend allowance section further than the edge of theencapsulation 104. In other words, the support member 116 may be placedunder the support layer 108 with some margin (denoted “B” in FIG. 6C)between the edge of the support layer 108 and the tip of the supportmember 116.

Similar to the support layer 108 place above the support member 116, thesupport layer 108 under the support member 116 should not be placed onthe rounded end portion of the support member 116. However, the edge ofthe support layer 108 under the support member 116 needs not be alignedwith the edge of the support layer 108 above the support member 116.Considering that the base layer 106 will be wrapped around the roundedend portion of the support member 116, spacing between the separatedsupport layers 108 on the bottom surface of the base layer 106 can beset with some alignment error margin. As such, the support layer 108 tobe placed under the support member 116 may be arranged on the bottomsurface of the base layer 106 such that the edge of the lower sidesupport layer 108 is positioned further away from bend allowance sectionthan the edge of the support layer 108 above the support member 116. Inthis setting, the distance (denoted “C” in FIG. 6C) between the edge ofthe lower side support layer 108 and the lower tip of the rounded endportion of the support member 116 can be greater than the distancebetween the edge of the upper side support layer 108 and the upper tipof the rounded end portion of the support member 116.

In some embodiments, the edge of the support layer 108 toward the bendallowance section can be provided with a flange, which extends evenfurther out toward the bend allowance section as shown in FIG. 6A. Theflange may be formed by cutting or otherwise patterning the supportlayer 108 to have a tapered edge. The flange can also be provided bystacking at least two support layers with their edges shifted from eachother. While omitted in FIGS. 6B and 6C, the flange can be provided inthose embodiments as well.

It should be appreciated that the configurations described above inreference to FIGS. 6A-6C are merely illustrative. Adhesive layers havingthe same thickness can be provided on the upper and the lower surfacesof the support member regardless of the position of the elongated bodyportion. Further, adhesive layers on both the upper surface and thelower surface of the support member can include a cushion layer.

Instead of employing a discrete support member 118, in some embodimentsof the flexible display 100, the support layer 108 may be provided witha thickened rounded end positioned under the base layer 106 in the bendallowance section. FIG. 6D is a schematic illustration showing anexemplary arrangement of the support layer 108 under the base layer 106at the bend portion of the flexible display 100. In this example, theend portion of the support layer 108 is thicker than the portion of thesupport layer 108 under the display area of the flexible display 100.Also, the thicker portion of the support layer 108 has a rounded edge,which substantially conforms to the curvature of the base layer 106 inthe bend allowance section. In this way, the rounded edge of the supportlayer 108 can serve as the discrete support member 116 employed in theembodiments depicted in FIGS. 6A-6C.

In this case, the support layer 108 can be formed of plastic materialsuch as polycarbonate (PC), polyimide (PI), polyethylene naphthalate(PEN), polyethylene terephthalate (PET), other suitable polymers, acombination of these polymers, etc. The rigidity of the support layer108 formed of such plastic materials may be controlled by the thicknessof the support layer 108 and/or by providing additives for increasingthe rigidity. As such, a portion of the support layer 108 correspondingto the substantially flat portion of the flexible display or to thedisplay area can have a different thickness from the portion of thesupport layer 108 corresponding to the bend portion of the flexibledisplay 100. It should be noted that the thickness of the support layermay be thicker in the bend portion of the flexible display 100 than thesubstantially flat portion of the flexible display 100 as the roundededge portion of the support layer 108 is used in providing the curvedsurface for the flexible base layer 106 to be wrapped around. Similar tothe support member 116 of the previously mentioned embodiments, thesupport layer 108 provided with the rounded edge portion can be formedin a desired color (e.g., black, white, etc.).

Unlike the embodiments where two separate support layers are provided atthe opposite ends of the bend allowance section, a single piece ofsupport layer 108D is used to support the base layer 106 in the bendportion of the flexible display 100. In addition to the cost savings andprocess simplification in manufacturing of the flexible display 100, theelimination of a separate support member 116 from the flexible display100 provides may provide various benefits as to the design of theflexible display 100. First of all, it is very unlikely that theencapsulation 104 will be extended out toward the bend allowance sectionpast the support layer 108D when using the end of the support layer 108Dto support the base layer 106 in the bend allowance section.Accordingly, any problems which might result from the misalignment ofthe encapsulation 104 in relation to the edge of the support layer 108on the separate support member 116 can be prevented.

Also, using a single piece of support layer 108D for supporting the baselayer 106 in the bend portion eliminates the needs for providingalignment error margins between separate pieces of the elements in thebend allowance section. For instance, the extra margins for ensuringthat the support layers are not placed over the rounded end portion ofthe support member 116 (e.g., margins B and C) are no longer needed.With the extra margin eliminated from the design of the bend portion,even a narrower bezel can be achieved in the flexible display 100.

The support layer 108D may be formed of any of the plastic materialsdescribed suitable for the support layer 108 and the support member 116.However, to provide the thicker rounded end portion in the support layer108D as shown in FIG. 6D, it is preferred that the support layer 108D isformed of a material suitable for an injection molding process or otherprocesses capable of forming the support layer 108 with an edge that issufficiently rounded to accommodate the curvature of the base layer 106in the bend allowance section.

Multi-Layered Conductive Lines

Several conductive lines are included in the flexible display 100 forelectrical interconnections between various components therein. Thecircuits fabricated in the active area and inactive area may transmitvarious signals via one or more conductive lines to provide a number offunctionalities in the flexible display 100. As briefly discussed, someconductive lines may be used to provide interconnections between thecircuits and/or other components in the central portion and the bendportion of the flexible display 100.

As used herein, the term conductive lines broadly refers to a trace ofconductive path for transmitting any type of electrical signals, powerand/or voltages from one point to another point in the flexible display100. As such, conductive lines may include source/drain electrodes ofthe TFTs as well as the gate lines/data lines used in transmittingsignals from some of the display driving circuits (e.g., gate driver,data driver) in the inactive area to the pixel circuits in the activearea. Likewise, some conductive lines, such as the touch sensorelectrodes, pressure sensor electrodes and/or fingerprint sensorelectrodes may provide signals for sensing touch input or recognizingfingerprints on the flexible display 100. Furthermore, conductive linescan provide interconnections between elements of the active area in thecentral portion and elements of the secondary active area in the bendportion of the flexible display 100. It should be appreciated that thefunctionalities of conductive lines described above are merelyillustrative.

Conductive lines in a flexible display 100 should be carefully designedto meet various electrical and non-electrical requirements. Forinstance, a conductive line may have a specific minimum electricalresistance level, which may vary depending on the type of signals to betransmitted via the conductive line. Some conductive lines may be routedfrom the substantially flat portion to the bend portion of the flexibledisplay 100. Such conductive lines should exhibit sufficient flexibilityto maintain its mechanical and electrical robustness. To this end, someconductive lines of the flexible display 100 may have a multi-layeredstructure.

FIGS. 7A and 7B each illustrates exemplary stack structure of themulti-layered conductive line. Referring to FIG. 7A, the conductive line120 has a multi-layered structure in which the primary conductive layer122 is sandwiched between the secondary conductive layers 124. Theprimary conductive layer 122 may be formed of material with a lowerelectrical resistance than that of the secondary conductive layer 144.Non-limiting examples of the materials for the primary conductive layer122 includes copper, aluminum, transparent conductive oxide, or otherflexible conductors.

The secondary conductive layer 124 should be formed of conductivematerial that exhibits sufficiently low ohmic contact resistance whenformed in a stack over the primary conductive layer 122. Low ohmiccontact resistance between the conductive layers is not the only factorin the selection of materials for the conductive layers in themulti-layered conductive line 120. While meeting the stringentelectrical and thermal requirements (e.g., resistance, heat generation,etc., the materials of the conductive line 120 should also satisfy theminimum mechanical stress requirement (e.g., Young's modulus). That is,both the primary conductive layer 122 and the secondary conductive layer124 should be formed of materials exhibiting sufficient flexibility.

Accordingly, in some embodiments, at least some of the conductive lines120 of the flexible display 100 may be formed with two or more of layersselected from aluminum (Al), titanium (Ti), molybdenum (Mo), Copper (Cu)layers. Examples of such combination include an aluminum layersandwiched between titanium layers (Ti/Al/Ti), an aluminum layersandwiched between upper and lower molybdenum layers (Mo/Al/Mo), acopper layer sandwiched between titanium layers (Ti/Cu/Ti) and a copperlayer sandwiched between upper and lower molybdenum layers (Mo/Cu/Mo).Of course, other conductive materials can be used for theprimary/secondary conductive layers.

Electronic device employing the flexible display 100, for instance awearable electronic device or a water submergible electronic device, mayexpose the flexible display 100 in a humid environment. In some cases,moist can reach the conductive line 120. Dissimilar metals and alloyshave different electrode potentials, and when two or more come intocontact in an electrolyte, one metal acts as anode and the other ascathode. The electro-potential difference between the dissimilar metalsaccelerates corrosion on the anode member of the galvanic couple, whichwould be the primary conductive layer 122 in the multi-layeredconductive line 120 (e.g., Al layer in the Ti/Al/Ti stack). The anodemetal dissolves into the electrolyte, and deposit collects on thecathodic metal.

When using a multi-layered conductive line 120 described above, anysurface that exposes both the primary conductive layer 122 and thesecondary conductive layer 124 may become a galvanic corrosioninitiation point. Accordingly, in some embodiments of the flexibledisplay 100, at least some conductive lines 120 is provided with astructure in which the outer surface of the primary conductive layer 122is surrounded by the secondary conductive layer 124 as shown in FIG. 7B.Such a configuration hinders the electrolyte from being in contact withboth the primary conductive layer 122 and the secondary conductive layer124, thereby minimizing loss of the primary conductive layer 122 bygalvanic corrosion.

Such a multi-layered conductive lines 120 can be created by firstdepositing the material for the primary conductive layer 122 (e.g., Al)over the secondary conductive layer 124 (e.g., Ti). Here, the secondaryconductive layer 124 underneath the primary conductive layer 122 mayhave greater width. Etch resist material is formed over the stack ofthese two layers and etched (e.g., dry etch, wet etch, etc.) to form theconductive line in a desired trace. After striping the etch resistancematerial, another layer of secondary conductive layer 124 (i.e., Ti) isdeposited over the patterned structure (i.e., Ti/Al). The width of thesecondary conductive layer 124 deposited over the primary conductivelayer 122 may be greater than the width of the primary conductive layer122 to cover the outer surface of the primary conductive layer 122.Another round of etching and striping of the etch resistance material isperformed to form the stack of a multi-layered conductive line in adesired conductive line trace design. It should be understood that themulti-layered conductive line formation processes described above aremerely an example. Accordingly, some processes may be added and/orskipped in making a multi-layered conductive line.

Bridged Conductive Lines

Manufacturing of the flexible display 100 can involve scribing a largeflexible polymer sheet into a base layer 106 of a desired shape andsize. Also, some parts of the base layer 106 become unnecessary as themanufacturing progresses, and such parts may be chamfered away. Someconductive lines on the base layer 106 laid across the scribing lineand/or the chamfer line can be cut during the scribing and/or chamferingprocesses. For instance, one or more conductive lines used for testingor temporarily operating the driving circuits, pixels and/or variousother components during manufacturing of the flexible display 100 may belaid across the scribe line or the chamfer line of the base layer 106.Such conductive lines may be referred to as the “test lines” in thepresent disclosure. Once the tests or other procedures involving the useof these test lines are completed, scribing and/or chamfering processescan be performed to remove the scribed/chamfered area along with theparts of the test lines placed thereon.

In some embodiments, a pad for receiving one or more signals may beprovided on one end of the conductive lines. The other end of theconductive line may be connected to the data lines of the pixels and/orsome of the driving circuits. Various signals can be supplied on theconductive line via the pads and transmitted to the destination via theconductive line to carry out the test procedures. These test pads maytake a considerable space on the base layer 106, and thus they can beplaced on the part of the base layer 106 to be scribed/chamfered away.

FIG. 8A illustrates a non-display area of the flexible display 100, inwhich a bend allowance section is provided. As shown, the test lines120_C and test pads 120_P can be placed in the non-display area wherethe bend allowance section is located. In particular, the test pads120_P can be provided in the area that is to be notched away by thechamfering process.

The non-display area with the bend allowance section may not havesufficient room to accommodate testing pads 120_P, especially ifconnection interfaces for connecting external printed circuits (e.g.,COF and/or PCB) are provided in that non-display area. In such cases,the test line 120_C may be routed across the bend allowance section.Further, the test line 120_C may be overlapped by other conductive linesprovided in the routing area, and it can cause undesired parasiticcapacitance issues.

Accordingly, in some other embodiments, the testing pads may be providedin the non-display area other than the ones provided with the connectioninterfaces for connecting printed circuit. As shown in FIG. 8B, thetesting pads 120_P can simply be placed outside the chamfer line of thebase layer 106 so that they are removed from the flexible display 100after the chamfering process.

Regardless of where the testing pads 120_P were placed, the part of thetest lines 120_C remaining on the base layer 106 will be extended untilthe scribed/chamfered edge of the base layer 106, and the exposedsurface of the test lines 120_T at the scribed/chamfered edge of thebase layer 106 can be highly susceptible to galvanic corrosion.

As mentioned above, corrosion at one point can grow along the conductiveline and cause various defects within the flexible display 100. In orderto suppress the growing of the corrosion, a bridge structure 120_B canbe provided in the conductive line (e.g., the test lines 120_C), whichis to be cut by the scribing or chamfering processes duringmanufacturing of the flexible display 100. More specifically, theconductive line 120_C can include at least two parts. The part of theconductive line extended to the scribed/chamfered edge of the base layer106 is separated apart from the rest of the conductive line remaining onthe base layer 106. These separated conductive line parts are connectedby a conductive bridge 120_B, which is arranged to be in contact witheach of the separated parts of the conductive line through contact holesin one or more the insulation layer(s).

Before a part of the conductive line on the base layer 106 is cut by thescribing/chamfering processes, signals can be transmitted between theseparated conductive line parts via the conductive bridge 120_B. Afterthe part of the conductive line is cut by the scribing/chamferingprocess, the corrosion which may start from the scribed edge or thechamfered edge is suppressed from growing along the conductive line dueto the space between the separated conductive line parts. Although thebridge 120_B is in contact with the separated parts of the conductiveline, the bridge 120_B is located in a different layer from theconductive line 120_C, and it hinders the growth of corrosion past thebridge 120_B.

FIG. 9A illustrates a cross-sectional view of an exemplary embodiment offlexible display 100 provided with bridged conductive lines. In theembodiment shown in FIG. 9A, the separated conductive line parts areprovided in the same metal layer as the gate electrode of at least someof the TFTs provided on the base layer 106. Also, the bridge can beprovided in the same metal layer as the source/drain electrodes of theTFTs. The interlayer dielectric layer (ILD) between the source/drainelectrodes and the gate electrode of the TFTs may also be providedbetween the bridge 120_B and the separated conductive line parts 120_C,and the bridge 120_C can be in contact with the conductive line parts120_C via contact holes in the ILD.

The gate insulation (GI) layer provided between the gate electrode andthe semiconductor layer of the TFTs may also be provided under theseparated parts of the conductive line. Optionally, the buffer layer 126and the active buffer layer under the semiconductor layer of the TFTscan be provided under the conductive line parts 120_C. The passivationlayer 128 on the source/drain electrode of the TFTs can be provided overthe bridge 120_B as well. As will be described in further detail below,these insulation layers provided on or below the bridge 120_B and theconductive line parts 120_C can be patterned to suppress crackpropagation in the wire traces.

It should be noted that the semiconductor layer as well as some of theinsulation layers provided in the TFT area may not be provided in thearea where the bridged conductive line is placed. As such, although theseparated conductive line parts 120_C and the gate electrode of the TFTsare provided in the same metal layer, they need not be in the same planelevel as each other. In other words, the gate electrode of the TFTs andthe conductive line parts 120_C can be formed by deposition of the samemetal layer, but their plane level may be different by the structure ofthe layers under the metal layer. Likewise, the bridge 120_B forconnecting the separated conductive line parts 120_C and thesource/drain electrodes of the TFTs can be provided in the same metallayer, yet be in a different plane level from each other.

FIG. 9B is a cross-sectional view illustrating another exemplaryembodiment of the flexible display 100 provided with bridged conductivelines. In the embodiment depicted in FIG. 9B, the bridge 120_B isprovided under the separated conductive line parts 120_C. Morespecifically, the bridge 120_B is provided in the same metal layer asthe gate electrode of the TFTs in the flexible display 100, and theconductive line parts 120_C are provided in the same metal layer as thesource/drain electrodes of the TFT. In this case, each of the separatedconductive line parts 120_C will be in contact with the bridge 120_Bthrough the contact holes in the insulation layer between the conductiveline parts 120_C and the bridge 120_B positioned thereunder.

In the embodiments depicted in FIGS. 9A and 9B, the metal layers, inwhich the conductive line parts 120_C and the bridge 120_B are formedin, are described in reference to the metal layers used for providingelectrodes of co-planar type TFT. However, it should be noted that theflexible display 100 can include TFTs with staggered and/or invertedstaggered structures (i.e., top gated or bottom gated staggered TFTs).Accordingly, metal layers for implementing the separated conductive lineparts 102_C and the bridge 120_B may vary based on the stack structureof the TFTs in the flexible display 100. Also, various insulation layersother than the ILD, for instance gate insulation layer, passivationlayer, planarization layer and the likes, may be provided in between theseparated conductive line parts 120_C and the bridge 120_B based on thestructure of the TFTs.

Furthermore, it should be appreciated that the layer for implementingthe conductive line parts 120_C and the bridge 120_B are not limited tothe layers used for the gate electrode or the source/drain electrodes ofthe TFTs in the flexible display 100. Any conductive layers in theflexible display 100 may be used to provide the conductive line parts120_C and the bridge 120_B so long as there is at least one insulationlayer between the conductive line parts 120_C and the bridge 120_B. Forexample, any one of the conductive line parts 120_C and the bridge 120_Bmay be implemented with an inter-metal layer, which may be used is someof the TFTs in the flexible display 100. Also, a touch sensor may beintegrated in the flexible display 100, and the conductive layer forimplementing the touch sensor can be used in providing any one of theconductive line parts 120_C and the bridge 120_B in the flexible display100. In embodiments of the flexible display 100 using oxide TFTs, themetal oxide layer used for providing the active layer of the TFT can bepatterned as the conductive line parts 120_C or the bridge 120_B. Posttreatment can be performed on the metal oxide layer patterned as theconductive line parts 120_C or the bridge 120_B to obtain a desiredconductivity.

Trace Design

A trace design of a conductive line is an important factor, which canaffect the conductive line's electrical and mechanical properties. Tomeet the electrical and mechanical requirements, some portion of aconductive line may be configured differently from another portion ofthe conductive line. As such, a portion of a conductive line at or nearthe bend allowance section of the flexible display 100 may be providedwith several features for bend stress management.

Bend stress management of the insulation layers near the conductive lineis just as important as the managing the strain of the conductive lineitself. Various insulation layers, such as the buffer layer 126, thepassivation layer 128, a gate insulation layer (GI layer) and aninterlayer dielectric layer (ILD layer) positioned below and/or abovethe conductive line 120 may include a layer of inorganic materials.Layers that are formed of inorganic material, for instance a siliconoxide layer and a silicon nitride layer, are generally more prone tocracks than the metal layers of the conductive line. Even when theconductive lines have a sufficient flexibility to cope with the bendstress without a crack, some of the cracks initiated from the insulationlayer can propagate into the conductive lines and create spots of poorelectrical contacts in the flexible display 100.

In addition to applying a trace design for reducing bend stress on aconductive line, some of the insulation layers above and/or below thelayer of conductive line may be patterned according to the trace designof the conductive line to minimize the chance of cracks. Variousinsulation layer patterning methods, such as wet etching and/or dryetching processes, can be used to form a trace of insulation layer thatcorresponds to the trace of a conductive line. Lack of insulation layer,especially the inorganic material based insulation layer around thetrace of a conductive line not only lowers the chance of crackgeneration, but it also cuts off the path for a crack propagation. Forconvenience of explanation, a trace of conductive line 120 and a traceof insulation layers covering at least some part of the conductive line120 are collectively referred to as the “wire trace” in the followingdescription.

As mentioned, a trace design for the conductive line and the insulationlayer covering the conductive line plays an important role in increasingthe robustness of the wire trace. Numerous parameters, ranging from athickness and a width of a wire trace to a length and a fan-out angle ofa wire trace segment with respect to the bending direction of theflexible display 100, are associated with the wire trace design. Inaddition to the aforementioned parameters, various other parametersregarding the conductive line 120 and the insulation layer trace arespecifically tailored based on the placement and the orientation of thewire trace within embodiments of the flexible display 100.

Strain on a wire trace from the bend stress will be greater as thedirection in which the wire trace extends is more aligned with thetangent vector of the curvature. In other words, a wire trace willwithstand better against the bend stress if the length of a wire tracesegment being parallel to the tangent vector of the curvature isreduced. No matter which direction the wire trace is extended to, therewill always be a portion in the wire trace that is measurable in thebending direction. However, a length for each continuous measurableportion (i.e., a segment) being aligned parallel to the bendingdirection can be reduced by employing a strain-reducing trace design inthe wire trace.

FIG. 10 illustrates some of the exemplary strain-reducing trace designs.Any one or more of a sign-wave, a square-wave, a serpentine, asaw-toothed and a slanted line trace designs illustrated in FIG. 10 canbe used for wire traces of the flexible display 100. Employing such astrain-reducing trace design increases the portion of the wire tracearranged in a slanted orientation with respect to the tangent vector ofthe curvature. This, in turn, limits the length of the wire tracesegment extending in a straight line parallel to the bending direction.

Since the cracks in the wire trace by bending of the flexible displaygenerally initiate from an inorganic insulation layer, it is imperativethat the length of the insulation layer trace being aligned with thetangent vector of the curvature is also minimized. In the single linestrain-reducing designs, the width and the shape of the conductive linetrace as well as the width of the patterned inorganic insulation layersinterfacing with the surface of the conductive line trace should be keptminimal.

The strain-reducing trace designs illustrated in FIG. 10 are merelyexemplary, and other trace designs for reducing the length of a wiretrace segment parallel to the bending direction may be used in variousembodiments of the flexible display 100. Further, it should be notedthat some wire traces may adopt different strain-reducing trace designfrom other wire traces in a flexible display 100 depending on theirelectrical and/or mechanical requirements. For instance, astrain-reducing trace design used for a data signal line may bedifferent from a strain-reducing trace design used for a power line.

To further improve robustness, a wire trace may employ a trace design inwhich the wire trace repeatedly splits and converges back in a certaininterval. In other words, a wire trace includes at least two sub-tracesarranged to form a trace design resembling a chain with a series ofconnected links. The angles of split and merge define the shape of eachlink, which allows to limit the length of the wire trace segmentmeasurable in straight line parallel to the bending direction.

Referring to FIG. 11A, the conductive line 120 includes sub-trace A andsub-trace B, which are split away from each other and merge back at eachjoint X. Between the first joint X(1) and the second joint X(2), a partof the sub-trace A is extended for a predetermined distance in a firstdirection angled away from the tangent vector of the curvature, andanother part of the sub-trace A is extended in a second direction. Thesub-trace B is arranged in a similar manner as the sub-trace A, but in amirrored orientation in reference to the tangent vector of thecurvature. The distances and directions in which the sub-traces arearranged between the two adjacent joints X define the shape and the sizeof the link in the chain as well as the open area surrounded by thesub-traces. In this example, the shape of the conductive line 120between the joint X(1) and X(2) (i.e., link) has a diamond shape with anopen area surrounded by the sub-trace A and the sub-trace B. Withadditional joints X, the conductive line 120 forms a chain of diamondshaped links, and thus the trace design may be referred to as thediamond trace design.

Compare to the non-split strain-reducing trace designs shown in FIG. 10,the strain-reducing trace design shown in FIG. 11A can providesignificant advantages in terms of electrical property. For instance,the wire trace provided with the split/merge trace design can providemuch lower electrical resistance than the wire traces employing themountain trace design, the sign-wave trace designs or other single linestrain-reducing trace designs of FIG. 10. In addition, sub-traces canserve as a backup electrical pathway in case one of the sub-traces isdamaged or severed by cracks.

The insulation layers covering the surfaces of the conductive line 120is also patterned in a trace design corresponding to the trace design ofthe conductive line 120. As such, the open area surrounded by thesub-trace A and the sub-trace B is free of the inorganic insulationlayer(s), or has thinner inorganic insulation layer(s) than the areasunder and/or above the trace of conductive line 120. As such, the lengthof the insulation layer trace measurable in straight line parallel tothe bending direction can be limited to reduce the chance of crackinitiation and propagation.

Various additional factors must be considered for the strain-reducingtrace designs based on a plurality of sub-traces. The split/merge anglesand the length of each sub-traces between two adjacent joints X shouldprovide an offset for the inorganic insulation layer at the joints X andat the outer corners where the sub-trace changes its direction betweentwo adjacent joints X. To put it in another way, the open area, which issurrounded by the split sub-traces between two joints X of the wiretrace, should have a size and a shape to minimize the length in which aninorganic insulation layer trace of the wire trace extending parallel tothe bending direction.

In the diamond trace design depicted in FIG. 11A, the buffer layer 126and the passivation layer 128 covering the trace of the conductive line120 are patterned with a predetermined margin from the outer trace(i.e., outer edge) of the conductive line 120. Other than the insulationlayers with the predetermined margin remaining to cover the conductiveline 120, the open area surrounded by the sub-traces A and B, which isdenoted as FA2, is free of the insulation layers. As such, a trace ofinsulation layers is formed in accordance with the trace design of theconductive line 120. The length of the open area without the insulationlayers measured in orthogonal direction from the bending direction isgreater than the width of the inorganic insulation layer trace at thejoint X measured in the same direction. In this setting, the open areaFA2 surrounded by the sub-traces A and B as well as the area next to thejoint X can be free of the inorganic insulation layers, or otherwiseprovided with a reduced number of inorganic insulation layers.

Referring to FIG. 11A, the insulation layer free area FA1 prohibits theinsulation layer of the sub-trace A and the sub-trace B between the twojoints X(1) and X(2) to be extended in a continuous straight line.Similarly, the insulation layer free area FA2 prohibits the insulationlayer between the two joints X(1) and X(2) to be extended in acontinuous straight line. Accordingly, the length of each segment of theinsulation layer trace being aligned to the tangent vector of thecurvature is minimized.

Further reduction in the length of the insulation layer trace aligned tothe tangent vector of the curvature can be obtained by reducing thewidth of the conductive line 120 and the margin of the insulation layerbeyond the edge of conductive line 120. It should be noted that theamount of reduction in the width of conductive line 120 is limited withthe single line strain-reducing trace designs depicted in FIG. 10because the reduction of conductive line width can make its electricalresistance too high for its particular use within the flexible display100. With the split/merge trace design of FIG. 11A, however, the widthof the conductive line 120 and the insulation layer trace can be reducedwhile providing sufficient electrical property.

Greater split/merge angle of the sub-traces with respect to the bendingdirection may allow to reduce the lengths of the conductive line 120 andthe insulation layer trace extending along the tangent vector of thecurvature to a greater extent. Accordingly, a lower chance of crackinitiation may be afforded in the wire trace by selectively increasingthe split/merge angle of sub-traces at high bend stress regions.

It should be noted that the split angle of the sub-traces can affect thedistance between the two adjacent joints X in the diamond trace design.The distance between the joints X need not be uniform throughout theentire wire trace. The intervals at which the trace splits and mergescan vary within a single trace of wire based on the level of bend stressexerted on the parts of the wire trace. The distance between the jointsX may be progressively shortened down for the parts of the wire tracetowards the area of the flexible display 100 subjected to higher bendstress (e.g., area having smaller bend radius, area having larger bendangle). Conversely, the distances between the joints X can progressivelywiden out towards the area subjected to lower bend stress.

Even with the strain-reducing trace design, the inevitable bend stressremains at certain points of the trace (i.e., stress point). Thelocation of stress point is largely dependent on the shape of the traceas well as the bending direction. It follows that, for a given bendingdirection, the wire trace can be designed such that the remaining bendstress would concentrate at the desired parts of the wire trace. Knowingthe location of the stress point in the wire trace, a crack resistancearea can be provided to the stress point to make the wire trace lastlonger against the bend stress.

Referring back to FIG. 11A, when a wire trace having the diamond tracedesign is bent in the bending direction, the bend stress tends to focusat the angled corners (i.e., the vertexes of each diamond shaped link),which are denoted as the stress point A and stress point B. As such,cracks tend to initiate and grow between the inner and outer edges ofthe wire trace. For instance, at the stress points A, a crack mayinitiate from the inner trace line 120(IN) and grow toward the outertrace line 120(OUT). Similarly, a crack may initiate from the outer wiretrace line 120(OUT) and grow toward the inner trace line 120(IN) at thestress points B.

Accordingly, the width of the conductive line 120 at the stress points Acan be selectively increased to serve as the crack resistance area. Asdepicted in FIG. 11A, the widths (W_(A), W_(B)) of the conductive line120 at the stress points A and B, which are measured in the directionperpendicular to the bending direction, may be longer than the width (W)of the conductive line 120 at the parts between the stress points A andB. The extra width at the stress points can make the conductive line 120hold out longer before a complete severance in the conductive line 120occurs by the growth of a crack at the stress points.

It should be reminded that the length for the continuous portion of theinsulation layer trace being aligned to the bending direction should bekept minimal. Increasing the width of the conductive line 120 at thestress points A and B may necessitate increase in the width of theinsulation layer trace at the respective area, which results inlengthening the insulation layer trace being aligned parallel to thebending direction.

Accordingly, in some embodiments, the width of the conductive line 120measured in the direction perpendicular to the tangent vector of thecurvature at the stress points A ranges from about 2.5 um to about 8 um,more preferably, from about 3.5 um to about 6 um, more preferably fromabout 4.5 um to about 8.5 um, and more preferably at about 4.0 um. Thewidth of the conductive line 120 at the stress points B should also bemaintained in the similar manner as the width of the conductive line 120at the stress points A. As such, the width of the conductive line 120 atthe stress points B may range from about 2.5 um to about 8 um, morepreferably, from about 3.5 um to about 6 um, more preferably from about4.5 um to about 8.5 um, and more preferably at about 4.0 um. Since thesub-trace A and the sub-trace B merges at the stress point B, the widthof the conductive line 120 at the stress points B may be longer thanwidth at the stress points A.

In some embodiments, one of the inner trace line 120(IN) and the outertrace line 120(OUT) may not be as sharply angled as the other trace lineat the stress points A to minimize the chance of crack initiating fromboth sides. In the embodiment depicted in FIG. 11A, the inner trace line120(IN) is more sharply angled than the outer trace line 120(OUT) at thestress points A. However, in some other embodiments, the outer traceline 120(OUT) may be more sharply angled than the inner trace line120(IN) at the stress points A. In both cases, the less sharply angledtrace line can simply be more rounded rather than being a straight lineas the outer trace line 120(OUT) depicted in FIG. 11A. Further, both theinner trace line 120(IN) and the outer trace line 120(OUT) at the stresspoints A can be rounded.

The wire trace may split into additional number of sub-traces, resultingseries of links arranged in a grid-like configuration. As an example, awire trace can be configured as a web of diamond trace shapes asillustrated in FIG. 11B. Such a trace design is particularly useful fora wire trace that transmit a common signal to multiple points or for awire trace that require a very low electrical resistance. For example, aVSS line and a VDD line in the flexible display 100 may have thegrid-like trace design, especially if such lines are arranged to crossover a bend allowance section. Neither the number of sub-traces nor theshapes of the sub-traces of the grid-like trace design are particularlylimited as the exemplary design depicted in FIG. 11B.

In some embodiments, the grid width can be reduced or increased inbetween two ends within the flexible display 100. Also, the grid-likewire trace shown in FIG. 11B can converge back to form the diamond traceshown in FIG. 11A or to form a non-split strain-reducing trace designshown in FIG. 10. In some cases, the size of each diamond-shaped traceof a grid-like wire trace may be larger than the size of eachdiamond-shaped trace of a diamond-chain trace to reduce the resistance.

Wire Trace Arrangement

Due to the portions angled away from the bending direction, a wire tracewith a strain-reducing trace design may necessitate a larger routingarea within the flexible display 100. In embodiments where a non-displayarea at the edge of the flexible display 100 is bent, the increase inthe routing area for accommodating the wire traces can actually increasethe size of the inactive area to be hidden under a masking.

Accordingly, wire traces applied with a strain-reducing trace design maybe arranged to facilitate tight spacing between adjacent wire traces.For instance, two adjacent wire traces with a strain-reducing tracedesign may each include a non-linear section, which would have a convexside and a concave side. The two adjacent wire traces can be arranged inthe flexible display such that the convex side of the non-linear sectionin the first wire trace is positioned next to the concave side thenon-linear section in the second wire trace. Since the spacing betweenthe two adjacent wire traces is limited by the shape and the size of thewire traces, the non-linear section in the strain-reducing trace designof the first wire trace may be larger than the non-linear section in thestrain-reducing trace design of the second wire trace. Of course, one ofthe first wire trace and the second wire trace may have a differentstrain-reducing trace design to better accommodate the non-linearsection of the other wire trace.

In some instances, two or more wire traces arranged next to each othermay each be applied with a strain-reducing trace design, and each of thewire traces may have a plurality of indented sections and distended. Insuch cases, the wire traces can be arranged such that the distendedsection of one of the wire traces to be positioned next to the indentedsections of the adjacent wire trace.

FIG. 12 illustrates an exemplary arrangement of multiple wire traces,each having the diamond trace design described above. The split of thesub-traces widens the layout of the wire trace to create the distendedsection, whereas merging of the sub-traces narrows the layout of thewire trace to create the indented section. Accordingly, in terms of itslayout, the indented section of the wire trace is at the joint X,whereas the distended section of the wire trace is at the point wherethe split/merge angles of the sub-traces change between two adjacentjoints X.

As shown in FIG. 12, position of the joints X in a first wire trace andthe joints X in a second wire trace are arranged in a staggeredconfiguration. In this arrangement, the vertexes of the diamond shapedlink at the distended section in the first wire trace are positionednext to the joints X at the indented sections of the adjacent wiretraces. Such a staggered arrangement of the wire traces may help inlowering the electrical noises on the wire traces due to close proximitybetween the wire traces, and thus the distance between the wire tracescan be reduced. Even a tight spacing between the wire traces may bepossible by arranging the distended section of a wire trace to bepositioned closer toward the indented section of the adjacent wiretrace. For instance, the vertexes at the wide parts of one wire race canbe placed in the open area FA1, which is created by the split/mergeangle and the length of the sub-trace in the adjacent wire trace. Assuch, the staggered arrangement allows to maintain certain minimaldistance between the wire traces while reducing the amount of spacetaken up by the wire traces.

Patterned Insulation Layer

As mentioned, it should be noted that cracks primarily initiate from theinorganic insulation layers. Accordingly, propagation of cracks can besuppressed by selectively removing inorganic insulation layers from theareas prone to cracks. To achieve this, one or more inorganic insulationlayers and/or stack of insulation layers including a layer of inorganicmaterial can be selectively etched away at various parts of the flexibledisplay 100.

For example, the insulation layer under the conductive line 120 can beetched away. The insulation layer under the conductive line 120 may bethe buffer layer 126, which may include one or more layers of inorganicmaterial layers. The buffer layer 126 may be formed of one or morelayers of a SiN_(x) layer and a SiO₂ layer. In one suitableconfiguration, the buffer layer 126 may be formed of alternating stacksof a SiN_(x) layer and a SiO₂ layer. The buffer layer 126 is disposed onthe base layer 126, but under the TFT.

To facilitate easier bending of the flexible display 100, a part of thebuffer layer 126 may etched away in the bend portion of the flexibledisplay 100. Accordingly, the buffer layer 126 formed on thesubstantially flat portion of the base layer 106 may be thicker than thebuffer layer 126 over the bend portion of the base layer 106. When thebuffer layer 126 is formed in a stack of multiple sub-layers, the bufferlayer 126 in the substantially flat portion of the flexible display 100may include one or more additional sub-layers than the buffer layer inthe bend portion of the flexible display 100.

For example, the buffer layer 126 in the substantially flat portion mayinclude multiple stacks of a SiN_(x) layer and a SiO₂ layer, and thebuffer layer 126 in the bend portion includes a single stack of aSiN_(x) layer and a SiO₂ layer. It is also possible to have only asingle layer of either a SiN_(x) layer or a SiO₂ layer in some part ofthe bend portion. In one suitable configuration, each SiN_(x) layer andSiO₂ layer in the buffer layer 126 may have a thickness of about 1000 Å.As such, the thickness of the buffer layer 126 in the bend portion ofthe flexible display may range from about 100 Å to about 2000 Å.

In the substantially flat portion of the flexible display 100,additional layer of inorganic layer may be provided immediately belowthe semiconductor layer of the TFT, which may be referred to as theactive buffer. In some embodiments, an inorganic layer, which is mostclosely positioned under the active layer of the TFT, may be muchthicker than the individual inorganic layers of the buffer layer 126.

The buffer layer 126 in the bend allowance section may be etched evenfurther to expose the base layer 106 while leaving the buffer layer 126intact under the conductive line 120. In other words, a recessed areaand a protruded area are provided in the bend portion of the flexibledisplay 100. The protruded area includes the buffer layer 126 providedon the base layer 106, whereas the recessed area has the base layer 106exposed without the buffer layer 126 disposed thereon.

In one exemplary configuration shown in FIG. 13A, the conductive line120 is positioned on the protruded area, and the passivation layer 128is positioned over the conductive line 120 on the protruded area.Although the passivation layer 128 may be temporarily deposited over therecessed area, the passivation layer 128 can be removed from therecessed area by a dry etch or a wet etch process. As such, the recessedarea can be substantially free of the passivation layer 128. Whenetching the passivation layer 128 from the recessed area, part of thebase layer 106 can be etched as well. Accordingly, the thickness of thebase layer 106 at the recessed area can be lower than that of the baselayer 106 elsewhere in the flexible display 100. When the buffer layer126 is etched away as shown in FIG. 13A, propagation of crack from onepart of the buffer 126 to another part of the buffer layer 126 can behindered by the space in the recessed area. Similarly, propagation ofcracks by the passivation layer 128 is also hindered by the space of therecessed area. Accordingly, damage to the conductive line 120 bypropagation of cracks can be reduced.

In another suitable configuration shown in FIG. 13B, the recessed areaincludes the base layer 106 that is etched to a certain depth, and theconductive line 120 is deposited on the base layer 106 of the recessedarea. In this setting, the portion of the conductive line 120 isdisposed within the base layer 106. Some part of the conductive line 120is also deposited on a part of the buffer layer 126 that provides theprotruded area. A passivation layer 128 can be deposited over theconductive line 120, and then etched away from the recessed area toexpose the conductive line 120 in the recessed area.

Accordingly, the passivation layer 128 remains on the conductive line120 positioned on the protruded area. In this configuration, thepassivation layer 128 remaining on the buffer layer 126 can inhibitgalvanic corrosion as it covers the cross-sectional side surface of themulti-layered conductive line 120. While cracks generated from thebuffer layer 126 may penetrate to the conductive line 120 on the wall ofhollow space in the buffer layer 126, but reaching the part of theconductive line 120 positioned within the base layer 106 will bedifficult.

When the conductive line 120 has the multi-layered structure discussedabove, the part of the conductive line 120 in the recessed area needsnot be covered by the passivation layer 128. With the passivation layer128 removed from the surface of the conductive line 120 in the recessedarea, crack propagation from the passivation layer 128 can also beprevented. Further, galvanic corrosion generally starts from the edge ofthe conductive line 120 on the buffer layer, and thus the passivationlayer 128 covering the edge of the conductive line 120 on the buffer 126may not be needed if the distance between the conductive line 120 on thebuffer layer 126 and the conductive line 120 in the base layer 106 issufficiently spaced apart from each other. The configurations shown inFIGS. 13A and 13B may be used for the wire traces in the bend allowancesection with the strain-reducing trace patterns of FIGS. 10, 11A and11B. In addition to the bend allowance section, in some embodiments, thepatterned insulation layer may also be provided in the routing areabetween the active area and the bend allowance section as well as therouting area between the COF bonding area and the bend allowancesection.

Further, the patterned insulation layer described above can be providedin the active area. However, removal of inorganic insulation layers nearthe TFTs of the flexible display 100 may affect the electricalcharacteristic of components in the flexible display 100. For instance,undesired threshold voltage shift of TFTs may result when some part ofthe buffer layer 126 is removed. In order to maintain the stability ofthe TFTs, an additional shield metal layer can be formed under thesemiconductor layer of the TFTs. The shield metal layer may be under thebuffer layer 126 or interposed between the inorganic layers of thebuffer layer 126. In some embodiments, the shield metal layer may beelectrically connected to the source electrode or gate electrode of theTFTs.

In addition to the patterning of insulation layers in various parts ofthe flexible display 100, other structural elements can be removed orsimplified in some areas of the flexible display 100 to facilitatebending. For example, the touch sensor layer 112, the polarization layer110 and the likes may be absent in the bend area of the flexible display100. Absence or simplification of these components and the layers wouldcreate a number of uneven surfaces where the wire trace may need tocross.

When a wire trace is laid over such an uneven surface, some parts of thewire trace may be placed on a different plane level from another partsof the wire trace. As the parts are on different plane levels, theamount and direction of bend stress and the strain resulting from thebend stress can differ even among the parts of the wire trace. Toaccommodate the difference, a strain-reducing trace design for the wiretraces can include a modified trace design for the portion of the wiretrace on the uneven surfaces.

FIG. 14A is an enlarged cross-sectional view showing an exemplarybackplane configuration for a flexible display 100, in which severalinsulation layers are removed from the bend portion to facilitate morereliable bending.

Several organic and inorganic layers may be formed in between the baselayer 106 and the OLED element layer 102. In this particular example,alternating stacks of SiN_(x) and SiO₂ layers can be disposed on thebase layer 106 to serve as the buffer layer 126. The semiconductor layerof a TFT may be sandwiched by an active-buffer layer and a gateinsulation layer that are formed of SiO₂ layer. The gate of the TFT isdisposed on an interlayer dielectric layer (ILD), and the source/drainof the TFT having the multi-layered structure as discussed above issandwiched between the ILD and a passivation layer. Here, the ILD may beformed of a stack of SiN_(x) and SiO₂, and the passivation layer isformed of SiN_(x). Then, a planarization layer is disposed over thepassivation layer so that the anode for the OLED can be disposedthereon.

As mentioned above, use of the strain-reducing trace design is not justlimited to the part of the wire traces within the bend portion. Also,the strain-reducing trace design can be applied to the part of the wiretraces in the routing areas outside the bend allowance section. Usingthe strain-reducing trace design for the wire trace in such routing areacan afford increased protection to the wire trace against the bendstress.

In the routing area, however, several layers of organic and/or inorganicmaterial layers between the base layer 106 and the OLED element layer102 may be absent to facilitate bending of the flexible display 100.Such organic and/or inorganic layers, including but not limited to theILD, the gate insulation layer, buffer layer, passivation layer,planarization layer, etc. may not be present in the bend portion of theflexible display 100. Some of these layers may have been removed fromthe area by several etching processes.

By way of example, several insulation layers on the buffer layer 126 maybe etched by a first etch process EB1, which is followed by the secondetch process EB2 that etches away the active buffer and a part of thebuffer layer 126 (e.g., a stack of a SiN_(x) layer and a SiO₂ layer).These etching processes create multiple stepped regions as shown in FIG.16A, with one or more of vertically sloped surfaces and horizontallyleveled surfaces, where the wire trace is disposed thereon. The wiretrace laid over the vertically sloped surfaces and horizontally leveledsurfaces would have several bent spots, such as EB1 area and EB2 area.

When bending the flexible display 100 in the bending direction, the wiretrace may experience more strain at or near the stepped region. Numeroustests and experiments indicate that the chance of a crack is especiallyhigh in the wire trace crossing over the stepped region between the EB1area and the EB2 area. Accordingly, in some embodiments, thestrain-reducing trace design for the wire trace has a reinforced portionat or near the stepped region between a high-leveled surface and alow-leveled surface provided by insulation layers of the flexibledisplay.

In the example shown in FIG. 14B, the wire trace has a simple straightline trace at its both ends. However, the part of the conductive line120 that crosses over the bent areas EB1 and EB2 is reinforced with amodified trace design. At the modified portion, the conductive line 120is provided with a wider width extra width W_(R) to ensure theperseveration of the conductive line 120 even if cracks initiate fromthe insulation layer near EB1 and EB2 areas. The distance D_(R) in whichthe conductive line 120 is provided with the modified trace designdepends on the thickness of the insulation layers etched by the etchprocesses as well as the distance between the first leveled surface(e.g., plane level at EB1) and a second leveled surface (e.g., planelevel at EB2).

Past the modified portion (i.e., reinforced portion), the wire trace isillustrated as having the strain-reducing trace design (i.e., diamondtrace design), which is previously described with FIG. 11A. It should beappreciated that the strain-reducing trace design of the wire traceapplied with the modified portion is not limited to the strain-reducingtrace design depicted in FIG. 14B. Various embodiments of thestrain-reducing trace design can include a modified trace design for theportion of the wire trace corresponding to the stepped areas of twodifferently leveled surfaces.

While this may not always be the case, the routing areas adjacent to thebend allowance section may be the substantially flat portions of theflexible display 100. In such cases, the EB1 and EB2 areas would bepositioned at or just outside start of the bend allowance section in thebend portion, and the wire trace may be provided with the reinforcedportion in its trace design.

The increased width W_(R) of the reinforced conductive line portion mayserve its purpose well at or near the beginning and the end of the bendallowance section where the curvature is relatively small. The widerwidth W_(R) of the wire trace and the length in which the modified traceportion is applied in the wire trace can increase the length of the wiretrace that is aligned parallel to the bending direction. This would makethe wire trace harder to hold out against the bend stress at the regionwith greater bend radius.

For this reason, the distance D_(R) in which the reinforced portion isshould be limited such that the reinforced conductive line portion doesnot extend too much toward the bend allowance section. Accordingly, thedistance D_(R) of the reinforced conductive line portion may be limitedsuch that the trace design of the reinforced conductive line portiondoes not extend beyond the bend allowance section where it is bent morethan a predetermined threshold bend angle. By way of an example, thereinforced conductive line portion may not extend beyond the point whereit is 30° curved away from the tangent plane of the curvature. Thethreshold bend angle may be less than 20°, for example 10°, and morepreferably less than 7°.

The wire trace, which is provided with the reinforced portion at thestepped areas, may extend across the bend allowance section and routedto pads for COF or other components of the flexible display 100. In suchinstances, additional stepped region (similar to EB1 and EB2) may existat or near the opposite end of the bend allowance section. Theconductive line at or near such bent spots may be reinforced in thesimilar manner as the modified portion of the wire trace at the oppositeend as shown in FIG. 14B. If desired, the reinforced conductive lineportion at or near the stepped regions at the opposite ends of the bendallowance section may have a different shape as depicted in FIG. 14B.

FIGS. 15A and 15B, each shows a cross-sectional view of a flexibledisplay along the line A-A′ marked in FIG. 1, according to an embodimentof the present disclosure. The configurations shown in FIGS. 15A and 15Bmay be representing the examples in which the gate-in-panel (GIP)circuit and the external printed circuit are provided on a differentside from each other. For instance, the GIP may be at the left and/orthe right side of the central active area, and the external printedcircuit may be at the top side and/or the bottom side of the centralactive area.

As mentioned above, the bend line of the flexible display 100 can beprovided, not just top and bottom edges, but also at the side edges ofthe flexible display 100. Accordingly, the inactive areas with the GIPcircuit can be the bend portions of the flexible display 100. In thiscase, the part of the base layer 106 where the GIP is disposed on iscurved away from the plane of the part of the base layer 106 where theactive area is provided therein. In other words, there is a bendallowance section provided between the GIP area and the active area. Thebend allowance section between the GIP area and the active area may beconfigured in a similar way as the bend allowance section between theactive area and the inactive area where the external printed circuit isattached thereto.

For instance, at least some of the conductive lines extending from theGIP circuit to the active area may have the strain-reducing trace designdescribed in the present disclosure. (i.e., the strain-reducing tracedesigns depicted in FIGS. 10, 11A-11B, 14A-14B and 20) In particular, aconductive line in the bend allowance section connecting a scan outterminal of a shift register's stage to the corresponding gate line inthe active area may be applied with any one of the strain-reducing tracedesigns discussed in the present disclosure and other relevant featuresassociated with the applied strain-reducing trace design.

Also, similar to the patterned insulation layers discussed above, theinsulation layers provided below and/or above the conductive line,especially the ones that are formed of inorganic materials, may bepatterned according to the trace of the conductive line. For instance,the buffer layer 126 and the passivation layer 128 provided under andover the conductive line between the GIP area and the active area can bepatterned as depicted in FIGS. 13A-13B and 14A-14B.

It should be remembered that the backplane of the flexible display 100may employ different types of thin-film transistors for differentcircuits implemented on the base layer 106. That is, some thin-filmtransistors can have a different stack structure from other thin-filmtransistors. Also, some can be configured as N-type transistors whilesome are configured as P-type transistors. Further, some thin-filmtransistors may employ different kinds of semiconductor materials fromsome of the other thin-film transistors on the same backplane.

Accordingly, the semiconductor layer of the TFTs in the GIP area may beformed of the low-temperature-poly-silicon (LTPS), while thesemiconductor layer of the TFTs in the active area may be formed of theoxide semiconductor such as indium-gallium-zinc-oxide (IGZO). Forsimplicity, only one of the TFTs from each of the active area and theGIP area are shown in FIGS. 15A and 15B. However, it should be notedthat additional TFTs will be included in each of the pixel circuits andthe GIP circuit for controlling the emission of the connected OLEDelement. In some embodiments, the entire TFTs implementing the GIPcircuit may be formed of the LTPS TFTs while the entire TFTsimplementing the array of pixel circuits in the active area are formedof the oxide TFTs. In some other embodiments, only some of the TFTs in apixel circuit and/or only some of the TFTs in a GIP circuit may have thesemiconductor layer that is different from other TFTs of the flexibledisplay 100. As such, the TFTs shown in the active area and the GIP areain FIGS. 15A and 15B may have the same kind of semiconductor layer(e.g., LTPS), but there may be another TFT in the active area, which hasa different kind of semiconductor layer (e.g., oxide) from the otherTFTs. Likewise, the TFT shown in the active area and the GIP area inFIGS. 15A and 15B may have the same kind of semiconductor layer, butthere may be another TFT in the GIP area, which has a different kind ofsemiconductor layer from the other TFTs.

When at least one of the GIP area and the active area includes an oxidesemiconductor based TFT and the other area includes an LTPS TFT, thelayer of oxide semiconductor can be patterned between the active areaand the GIP area as lines laid between the GIP area and the active area.Post treatments, such as plasma treatment for increasing the carrierconcentration or other implantation and/or thermal annealing processes,can be performed on the patterned lines of the oxide semiconductor toturn them into conductive lines. In other words, when the backplane ofthe flexible display is implemented with multiple kinds of semiconductormaterials including the oxide semiconductor, the metal oxidesemiconductor layer can be patterned and selectively turned intoconductive lines in the flexible display 100. By way of an example, theconductive lines in the bend allowance section may be formed from themetal oxide semiconductor layer that is turned into the conductinglines.

As for the stack structure of the TFTs in the GIP area and the activearea, TFTs implementing the GIP and the TFTs implementing the pixelcircuit may both have the co-planar structure as shown in FIG. 15A. Inanother suitable embodiment of the flexible display 100, however, theTFTs implementing the GIP may have the co-planar structure, whereas theTFTs implementing pixel circuit have the bottom gate structure asdepicted in FIG. 15B. It is also possible that the TFTs implementing theGIP have the bottom gate structure and the TFTs implementing the pixelcircuit have the co-planar structure.

While the active areas in FIGS. 15A and 15B are shown as the one in thecentral portion of the flexible display, it should be noted that the GIPmay be provided in the inactive area adjacent to a secondary activearea, which is to be disposed in the area bent from the plane of anotheractive area (e.g., the central active area). For example, the bend angleof the bend allowance section between the first active area and thesecondary active area may be 90 degrees, and the bend angle of the bendallowance section between the second active area and the GIP area may be90 degrees. In this case, the part of the base layer 106 where the GIPis disposed in would be positioned under the plane of the first activearea.

In FIGS. 15A and 15B, the organic light-emitting layer, cathode, andetc. of the OLED element as well as layers of other components above theOLED element are omitted from the drawing for convenience. It should beappreciated that the GIP area can be formed in a pair, for instance oneon the left side and the other one on the right side of the active areaas shown in FIG. 1. The GIP area can also be formed in just one side ofan active area included in the flexible display 100. For instance, theremay be a GIP circuit provided on one side of a central active area forthe central active area, and there may be another GIP area on one sideof a secondary active area for the secondary active area.

In some embodiments, a bend allowance section may be provided betweenthe GIP area and the area positioned even further out toward the scribeline of the base layer 106, which may be referred in the presentdisclosure as the GIP input signal line area. Various signal lines,including but not limited to, the data signal lines from the displayD-IC and the VDD/VSS lines from the power supply unit and/or othercomponents of the flexible display 100 disposed on some other part ofthe base layer 106 or on a separate printed circuit attached to the baselayer 106, may be routed in the GIP input signal line area. Additionalnumber of signal lines may need to be placed in the GIP input signalline area as the number of pixels managed by the GIP circuit increases.

Accordingly, a bend allowance section can be provided between the GIPinput signal line area and the GIP area so that the GIP input signalline area can be bent away from the plane of the base layer 106 with theGIP area. Similar to the conductive lines in the bend allowance sectionbetween the GIP area and the active area discussed above in reference toFIGS. 15A and 15B, conductive lines extending across the bend allowancesection between the GIP input signal line area and the GIP area canconnect the GIP input signal lines to the corresponding part of the GIP.This configuration may be particularly useful if providing a bendallowance section between the GIP area and the active area is notfeasible or desired.

Areas near the processing line (e.g., scribing line, chamfer line) ofthe flexible display 100 may be another spots vulnerable to cracks. Forinstance, cracks can initiate from the insulation layers during cuttingthe base layer 106 or otherwise trimming a portion of the base layer 106into a desired shape. Chamfering of the base layer 106 can be performedafter other elements have been disposed on the base layer 106. Forinstance, the encapsulation 104 and the polarization layer 110 can beplaced on the base layer 106 corresponding to the active area. Variousother components can be provided on the OLED element layer 102 prior toscribing and/or chamfering a part of the base layer 106. Also, anexternal printed circuit 134 can be attached to the base layer beforechamfering of the base layer. If desired, additional external circuitcan be attached to the printed circuit 134 that is already attached tothe base layer 106. Moreover, the micro-coating layer 132 may bedisposed in the bend allowance section(s) of the flexible display 100.Some of the components provided under the base layer 106, for instancethe support layer 108, may also be arranged in their respective positionof the base layer 106 before performing the chamfering process.

To reduce the possible damage to the components of the flexible display100 by the processes related to trimming of the base layer 106, in someembodiments of the flexible display 100, one or more selectivecomponents disposed above the base layer 106 may be configured not toextend across the processing line of the base layer 106.

For instance, laser can be used to chamfer the base layer 106, theencapsulation (BFL) 104, the polarizer layer 110, and other layers in inthe flexible display 100 into a desired size and shape. Laser may be,for example, a continuous Wave (CW) or pulsed laser that produces lightat wavelengths from about 150 nm to about 20 microns (e.g., light atultraviolet, visible, or infrared wavelengths), and, more preferably alaser that produces infrared light at a wavelength in the range of 1 to20 microns, 1 to 12 microns, or 9 to 12 microns. In the infraredspectrum, high-power laser sources are widely available and mostpolymers are at least somewhat opaque and able to readily absorbincoming laser light. An example of a laser type that may be used forlaser is a carbon dioxide (CO₂) laser that produces light at one or morewavelengths in the range of about 9.2 to 11.4 microns). Other types oflasers may be used and other wavelengths of laser light may begenerated. For example, laser may be a diode laser, a solid state laser,a gas laser other than a CO₂ laser, or any other suitable type of laser.

In a typical scenario, laser may produce about 10 to 100 W of outputpower or other suitable amounts such as less than 50 W of power, morethan 20 W of power, etc. Beam may be focused to a spot on workpiece thathas a spot size (e.g., a 1/e² diameter) of about 100 to 500 microns indiameter. Under laser illumination conditions such as these, componentsof the flexible display 100 such as polarizer layer 110, the base layer106, encapsulation (BFL) 104 and other layers in in the flexible display100 will be cut (e.g., by thermal disassociation of the bonds in thepolymer material or other decomposition mechanisms such as ablation).

Some components of the flexible display 100 may be arranged on the baselayer 106 so that it is extended across the chamfer line. In such cases,the intensity of the laser used during the chamfering process can beincreased to provide throughput needed to cut through the layers belowthe chamfer line. If desired, the laser can be scanned along the chamferline for additional iterations to cut through the layers under thechamfer line.

In some cases, however, increasing the intensity of the laser output maynot be feasible because the heightened power can cause undesired damageto some components of the flexible display 100. That is, chamfering withthe laser of increased intensity may deliver the amount of energy (e.g.,heat energy), which may be too much for some of the layers under thechamfer line, resulting in various defects in the flexible display. Byway of an example, increased intensity of the laser may generate cracksin some insulation layers formed of inorganic materials, such as thebuffer layer 126, the passivation later 128 and the ILD, creating apassage which oxygen and moisture can permeate through to damage theTFTs and OLED elements of the flexible display 100. As a means fordamage control in the chamfering process, the number of scanning alongthe chamfer line with the laser can be increased while limiting theintensity of the laser. One of the obvious drawback of increasing thescanning iterations is the extra time necessary for completing thechamfering process.

Accordingly, in some embodiments of the flexible display 100, somecomponents of the flexible display 100 can be provided in a size and/orin a shape so that they are positioned away from the chamfer line. FIG.16B is an enlarged top view showing an exemplary configuration of achamfered corner and a notch provided in an embodiment of flexibledisplay shown in FIG. 16A.

As shown in FIG. 16B, a corner of the flexible display 100 can bechamfered along the chamfer line. As illustrated by the dotted line, thepart of the encapsulation (barrier film layer: BFL) 104 covering theactive area on the base layer 106 is extended over the chamfer line, andthus chamfered together with the base layer 106. On the contrary, thepolarization layer 110 disposed on the encapsulation 104 is arranged notto extend over the chamfer line, and thus the polarization layer 110 isnot cut by the laser cutting of the encapsulation 104 and the base layer106 along the chamfer line.

In this regard, the polarization layer 110 may be scribed in a size suchthat the “Corner (A)” of the polarization layer 110 does not extendacross the chamfer line. In another embodiment, the polarization layer110 can be provided with a rounded corner, as the “Corner (B)” shown inFIG. 16B. In yet another embodiment, the polarization layer 110 can beprovided with a corner that is similar to the chamfered corner of theflexible display 100. That is, the corner of the polarization layer 110may be pre-cut in the same or a similar chamfer angle as the corner ofthe flexible display 100. For example, the corner of the polarizationlayer 110 at the chamfered corner of the flexible display 100 may beprovided with a cutout portion similar to the chamfered corner of theflexible display 100, which is denoted as “Corner C1” in FIG. 16B. Samestyled corner (i.e., “Corner C1”) can be used for the corner of theplanarization layer 110 at the notch of the flexible display 100. Insome embodiments, the corner of the planarization layer 110 at the notchof the flexible display 100 can be chamfered similar to the chamfer linefor creating the notched area in the flexible display 100, denoted as“Corner (C2)” in FIG. 16B.

Prior to placing the polarization layer 110 on the encapsulation 104,laser chamfering or grinding can be performed to make the corners of thepolarization layer 110 as the “Corner (B)” or “Corner (C1, C2).” With“Corner (B)” and “Corner (C1, C2)”, a larger sized polarization layer110 can be used in the flexible display 100 as compared to thepolarization layer 110 provided with “Corner (A).”

Since the laser for chamfering the encapsulation 104 and the base layer106 does not have to cut through the polarization layer 110, intensityof the laser can be lowered without having to increase the scaniterations along the chamfer line. Therefore, the scribing and thechamfering of the base layer 106 can be performed more efficiently whilereducing the chance of defects along the chamfered line.

Cracks generated at the far end of the flexible display 100 canpropagate towards central portion. As such, if cracks are generated atthe chamfer line of the flexible display 100, it can propagate into thebending area and the routing areas adjacent to the bending area. In somecases, cracks from the scribing lines at the inactive areas provided ina flat central portion of the flexible display 100 can propagate towardthe active area and damage various circuits in the inactive areas, suchas the GIP.

Accordingly, selective areas along one or more scribing lines of theflexible display 100 may be substantially free of inorganic materiallayers. Referring back to FIG. 16A, area at one or more edges of thebase layer 106 in the flexible display 100, denoted as “the scribe lineetch area,” may be etched so that the area is substantially free ofinsulation layers of inorganic materials such the buffer layer 126. Inthe scribe line etch areas, the base layer 106 may be exposed or only apredetermined minimal thickness of the buffer layer 126 may remain.Although the scribe line etch areas are marked at the top edge and thebottom edge of the flexible display 100 in FIG. 16A, the location, thesize and the shape of the scribe line etch area are not particularlylimited as shown in FIG. 16A. The scribe line etch area can be providedat only at one of the top and bottom edges, provided at the side edgesor provided at all edges around the active area of the flexible display100. When the scribe line etch areas are provided at the side edges ofthe flexible display 100, one or more insulation layers, especially theinorganic insulation layers, may be etched from the edges of theflexible base layer next to the GIPs. In an embodiment in which theflexible display 100 is provided with a round shaped base layer 106, thescribe line etch area may be provided at the periphery of the activearea.

Several side crack stopper structures may also be provided in the areabetween the edge (i.e., scribed line/chamfered line) and the active areain a central portion of the flexible display 100. For instance, arecessed channel can be formed in the inactive area by etching theinsulation layers as shown in FIG. 16A (provided on the left side edge).Also, a dummy wire trace pattern may be disposed in the inactive area tochange the direction of crack propagating from the outer edge of theflexible display 100 toward the circuits in the inactive area. Suchcrack stopper structures can be provided between a circuit (or otherfragile elements) positioned in the inactive area and the outer edge ofthe flexible display 100. For example, a metal trace having astrain-reducing trace design and insulation layer covering the metaltrace can be formed between the GIP and the edge of the flexible display100 as depicted in FIG. 16A (provided on the right side edge). While therecessed channel and the dummy wire trace pattern are provided on theleft and right sides, respectively, such crack stopper structures can beprovided in the top and bottom sides as well.

It should be noted that the recessed channel on the left side of theactive area can also be provided on the right side of the active area.Likewise, the dummy wire trace with the strain-reducing pattern providedon the right side of the inactive area can also be provided on the leftside of the inactive area. In some embodiments, both the recessedchannel and the metal trace having the strain-reducing pattern can beprovided on one or more sides of the active area. In this configuration,the cracks propagating from the outer edge of the inactive area in thedirection towards the GIP may change its course due to the angle of thediamond metal/insulation trace formed before the GIP.

Patterning of insulation layers, especially the inorganic insulationlayers, can also be performed in the routing area between the activearea and the bend allowance section as well as the routing area betweenthe connection interface and the bend allowance section. Further, theinorganic material layers may be removed from at least some part ofareas adjacent to the chamfered lines so that cracks do not propagatefrom the chamfered line toward the conductive lines 120.

FIG. 16C is an enlarged view of lower left corner of the flexibledisplay near the notched area. In order to reduce crack initiation andpropagation from the inorganic layers near the chamfered line, theinsulation layer is etched in the area between the wire trace (e.g.,VSS/VDD line) to the chamfered line. In particular, the buffer layer 126disposed on the base layer 106 in the area between the chamfered lineand the conductive line 120 in the bend allowance section, which isclosest to the chamfer line (e.g., VSS/VDD line) can be removed. In thisarea, the base layer 106 may be exposed or buffer layer 126 with alimited thickness (i.e., thinner than the buffer layer 126 under theconductive line 120) may remain. Accordingly, crack initiation andpropagation from the chamfered line can be hindered by the buffer layeretched area.

When etching the buffer layer 126 near the chamfer line, a stripe ofbuffer layer 126 can be configured to remain between the chamfered lineand the wire trace closest to the chamfered line as depicted in FIG.16C. This stripe of buffer layer can serve as a dam for inhibitingmoistures of other foreign material from reaching the wire trace fromthe chamfered side of the flexible display 100.

The aforementioned buffer layer etched area can also be applied in therouting area between the chamfer line and the closest wire trace. Thestripe of buffer layer 126 may also be provided in the routing area.Further, the buffer layer 126 under the conductive lines 120 and thepassivation layer 128 on the conductive lines 120 can be patterned tocorrespond to the trace of the conductive lines 120 throughout therouting area to further reduce the chance of crack propagation by theinorganic insulation layers in the routing areas next to the bendallowance section. For instance, the configuration of wire tracestructures depicted in FIGS. 10, 11A-11B, 12, 13A-13B and 14A-14B mayalso be applied to the wire traces in the routing areas.

FIG. 16D is an enlarged view near the notched area of the flexibledisplay 100, provided with another type of crack stopper structure. Inthis embodiment, an auxiliary conductive line 130 having the diamondtrace pattern is provided between the chamfered line and the wire trace(e.g., VSS/VDD). The buffer layer 126 under the auxiliary conductiveline 130 and the passivation 128 on the auxiliary conductive line 130can be etched in the similar manner as depicted in FIGS. 13A and 13B.Accordingly, the auxiliary conductive line 130 may inhibit propagationof cracks from the chamfered line to the wire trace. The auxiliaryconductive line 130 may be a floating line. If desired, the auxiliaryconductive line 130 may extend outside the routing area towards thebottom edge of the flexible display 100. In some embodiments, theauxiliary conductive line 130 may be in contact with adjacent conductiveline 120. In addition to the auxiliary conductive line 130, the stripeof buffer layer 126 may also be provided to stop moisture or otherforeign materials traveling towards the auxiliary conductive line 130.

Although the polarization layer 110 has been described as the component,which is arranged not to cross over the processing line of the baselayer 106, various other components of the flexible display 100 can beconfigured in the similar way as the polarization layer 110 discussedabove in reference to FIG. 16B. Non-limiting examples of the componentsin the flexible display 100, which may be configured in the similar wayas discussed above, include a barrier film layer, a touch sensor layerand an adhesive layer. Further other optical sheet layers, such as alight guide panel, a prism sheet, a light extraction sheet, a colorconversion/enhancing layer (e.g., quantum-dot/rod layer, may be arrangedin the flexible display 100 such that a clearance is provided along theprocessing line of base layer.

Micro-Coating Layer

With the absent of various layers in the bend portion of the flexibledisplay 100, a protective layer may be needed for the wire traces,especially for the wire traces in the bend allowance section of theflexible display 100. Also, the wire traces in the bend portion can bevulnerable to moistures and other foreign materials as the inorganicinsulation layers can be etched away from in the bend portion of theflexible display 100. In particular, various pads and conductive linesfor testing the components during manufacturing of the flexible display100 may be chamfered, and this can leave the conductive lines extendedto the notched edge of the flexible display 100. Such conductive linescan be easily corroded by moistures, which can be expanded to nearbyconductive lines. Accordingly, a protective coating layer, which may bereferred to as a “micro-coating layer” can be provided over the wiretraces in the bend portion of the flexible display 100.

The micro-coating layer 132 may be coated over the bend allowancesection in a predetermined thickness to adjust the neutral plane of theflexible display 100 at the bend portion. More specifically, addedthickness of the micro-coating layer 132 at the bend portion of theflexible display 100 can shift the plane of the wire traces closer tothe neutral plane.

In some embodiments, the thickness of the micro-coating layer 132 in thearea between the encapsulation 104 and the printed circuit 134, which ismeasured from the surface of the base layer 106, may be substantiallythe same as the thickness of the encapsulation 104 on the base layer 106to the top surface of the encapsulation 104.

The micro-coating layer should have sufficient flexibility so that itcan be used in the bend portion of the flexible display 100. Further,the material of the micro-coating layer should be a curable materialwith low energy within a limited time so that the components under themicro-coating layer are not damaged during the curing process. Themicro-coating layer 132 may be formed of a photo-curable acrylic (e.g.,UV light, Visible light, UV LED) resin and coated over the desired areasof the flexible display 100. In order to suppress permeation of unwantedmoistures through the micro-coating layer, one or more getter materialmay be mixed in the micro-coating layer.

Various resin dispensing methods, such as slit coating, jetting and thelike, may be used to dispense the micro-coating layer 132 at thetargeted surface. In way of an example, the micro-coating layer 132 canbe dispensed by using a jetting valve. The dispensing rate from thejetting valve(s) may be adjusted during the coating process for accuratecontrol of the thickness and the spread size of the micro-coating layer132 at the targeted surface. Further, the number of jetting valves indispensing the micro-coating layer 132 over the desired area is notlimited, and it can vary to adjust the dispense time and the amount ofspread on the dispensed surface before the micro-coating layer 132 iscured.

FIG. 17A illustrates one suitable exemplary configuration of themicro-coating layer 132 in an embodiment of flexible display 100. Asmentioned, the micro-coating layer 132 can be coated in the area betweenthe encapsulation 104 and the printed circuit 134 attached in theinactive area. Depending on the adhesive property of the micro-coatinglayer 132 and the amount of bend stress, however, the micro-coatinglayer 132 can be detached away from the encapsulation 104 and/or theprinted circuit 134. Any open space between the micro-coating layer 132and the encapsulation 104 or the printed circuit 134 can become a defectsite where moisture can permeate through.

Accordingly, in some embodiments, the micro-coating layer 132 can beoverflowed onto a part of the encapsulation 104 as shown in FIG. 17A.That is, the top surface of the encapsulation 104 at its edge can becoated with the micro-coating layer 132. The additional contact area onthe surface of the encapsulation 104 coated by the micro-coating layer132 suppresses the micro-coating layer 132 from fall apart from theencapsulation 104 by the bend stress. The enhanced sealing provided bythe micro-coating layer 132 at the edge of the encapsulation 104 canreduce corrosion of the wire traces at the bend portion of the flexibledisplay 100. Similarly, the micro-coating layer 132 can be overflowedonto at least some part of the printed circuit 134 for improved sealingby at the edge of the printed circuit 134.

Referring to FIGS. 17B and 17C, the width of the area on theencapsulation 104 coated with the micro-coating layer 134 is denoted as“Overflow_W1”, and the width of the area on the printed circuit 134coated with the micro-coating layer 134 is denoted as “Overflow_W2.” Thesizes of the micro-coating layer 134 overflowed areas on theencapsulation 104 and the printed circuit 134 are not particularlylimited and may vary depending on the adhesiveness of the micro-coatinglayer 132.

As shown in FIG. 17B, the flexible display 100 may include a portionwhere the micro-coating layer 132 on the encapsulation 104 is spacedapart from the edge of the polarization layer 110. In some embodiments,however, the flexible display 100 may include a portion where themicro-coating layer 132 on the encapsulation 104 is in contact with thepolarization layer 110 disposed on the encapsulation 104 as depicted inFIG. 17C.

The spreading dynamic of the micro-coating layer 132 on the dispensedsurface depends on the viscosity of the micro-coating layer 132 as wellas the surface energy where the micro-coating layer 132 is dispensed. Assuch, the micro-coating layer 132 overflowed into the encapsulation 104may reach the polarization layer 110. The micro-coating layer 132 incontact with the sidewall of the polarization layer 110 can help inholding the polarization layer 132 in place. However, the micro-coatinglayer 132 reaching the sidewall of the polarization layer 114 may climbover the sidewall of the polarization layer 110. Such sidewall wettingof the micro-coating layer 132 can create uneven edges over the surfaceof the polarization layer 132, which may cause various issues in placinganother layer thereon. Accordingly, the amount of the micro-coatinglayer 134 dispensed on the targeted surface can be adjusted to controlthe width of the micro-coating layer 134 on the encapsulation layer 114.Further, the micro-coating layer 132 may be dispensed such that onlysome of the selective areas of the polarization layer 110 are in contactwith the micro-coating layer 132.

In one suitable configuration, the micro-coating layer 132 may be incontact with the polarization layer 110 at the two opposite corners(denoted “POL_CT” in FIG. 17A) while the micro-coating layer 132 betweenthe two corners does not reach the edge of the polarization layer 110.The micro-coating layer 132 between the two opposite corners (POL_CT)only covers up to some part of the encapsulation 104. After the bendingprocess, the part of the flexible display 100 where the micro-coatinglayer 132 is spaced apart from the polarization layer 110 may beconfigured as shown in FIG. 18A. In the region where micro-coating layer132 is configured to be in contact with the polarization layer 110, theflexible display 100 may be configured as shown in FIG. 18B.

The micro-coating layer is not perfectly impermeable to oxygen andparticularly not to moisture, so the micro-coating layer provided in theflexible display 100 will generally have some finite permeation rate.Gases and moistures that permeate through the micro-coating layer 132can react with the conductive lines at the sites of reaction. The gassesand moisture that permeate through the seal, which is provided by themicro-coating layer, may react with, for example, valley patternsremaining on the printed circuit 134 or the conductive lines at thescribed/chamfered edge of the base layer 106. Because the micro-coatinglayer 132 is disposed over the bend allowance section, the micro-coatinglayer 132 can be pulled away from the surface it was originallyattached, and leave the conductive lines vulnerable to the gasses andmoisture. Eventually, the sites of reaction reach some specifiedquantity, and render the flexible display 100 inoperable.

Employing getter materials within the micro-coating layer 132 can extendthe useable lifetime of the device. These getter materials absorb and/orreact with the water vapor that would otherwise corrode the conductivelines. Accordingly, in some embodiments, multiple kinds of micro-coatinglayers can be used in the flexible display 100. More specifically, aplurality of micro-coating layers can be provided over a bend allowancesection between a first portion and a second portion of the flexibledisplay apparatus 100.

In the embodiment shown in FIG. 19A, the first micro-coating layer132(A) can be coated over the wire traces in the bend allowance sectionof the flexible display 100, and the second type of micro-coating layer132B may be coated over the first type of micro-coating layer 132A. Oneof the first micro-coating layer and the second micro-coating layerincludes one or more of getter materials to reduce permeation ofmoisture. Examples of getter materials that can be included in themicro-coating layer include silica particles, zeolite, zeolitic clays,CaO particles, BaO particles, Ba metals and so on. In some embodimentsof the invention, one or more of the following thermally activatedgetters may be used: Zeolitic clay, Barium Oxide, Calcium Oxide andother reactive or water absorbing oxides, activated carbon or otherabsorptive organic or inorganic materials.

In one suitable configuration, the first micro-coating layer 132A mayinclude one or more getter materials to reduce permeation of moisture inthe bend allowance section. In another configuration, the secondmicro-coating layer 132B, which is the outer layer among the pluralityof micro-coating layers, may include one or more getter materials.

Also, in some embodiments, the first micro-coating layer 132A underneaththe second micro-coating layer 132B is extended further and providedover at least some part of the encapsulation 104. Likewise, the firstmicro-coating layer 132A may be extended further and provided over atleast some part of the printed circuit 134 at the opposite end of thebend allowance section as shown in FIG. 19B. In addition, the firstmicro-coating layer 132A coated over the bend allowance section can becoated over both the part of the encapsulation 104 as well as the partof the printed circuit 134. The first micro-coating layer 132A coated onthe part of the encapsulation 104 and/or the printed circuit 134 canprovide stronger adhesion to the encapsulation and/or the printedcircuit 134 for improved sealing at the respective areas.

In some cases, the second micro-coating layer 132B on the firstmicro-coating layer 132A may provide stronger adhesion with the surfaceof the encapsulation 104 and/or the printed circuit 134 than the firstmicro-coating layer 132A. Accordingly, the second micro-coating layer132B on the first micro-coating layer 132A may be coated over at leastsome part of the encapsulation 104 and/or at least some part of theprinted circuit 134 for improved sealing at the edges of theencapsulation 141 and the printed circuit 134 as depicted in FIGS.17A-17C. If desired, both the first and second micro-coating layers maybe provided on at least some part of the encapsulation 104 and/or theprinted circuit 134.

Rather than coating the multiple micro-coating layers over the bendallowance section, different types of micro-coating layer can beselectively used in different regions in between two portion of theflexible display apparatus 100. For instance, the micro-coating layerprovided near the edge of the encapsulation 104 and/or the printedcircuit 134 may be different from the micro-coating layer provided inthe area between the encapsulation 104 and the printed circuit 134.

In the embodiment shown in FIG. 20A, the region over the bend allowancesection is coated with a first type of micro-coating layer 132(A).Another type of micro-coating layer 132(B) is coated in the regions nextto the region coated with the first type of micro-coating layer 132(A).More specifically, the second type of micro-coating layer 132(B) isprovided in the region between the encapsulation 104 and the regioncoated with the first type micro-coating layer 132(A). Likewise, thesecond type of micro-coating layer 132(B) is provided in the regionbetween the printed circuit 134 and the region coated with the firsttype of micro-coating layer 132(A).

When cured, the first type of micro-coating layer 132(A) may be moreflexible than the second type of micro-coating layer 132(B). The secondtype of micro-coating layer 132(B) needs not be as flexible as the firsttype of micro-coating layer 132(A) since the regions coated by thesecond type of micro-coating layer 132(B) has less curvature than theregion coated with the first type of coating layer 132(A). Although thesecond type of micro-coating layer 132(B) may not be as flexible as thefirst type of micro-coating layer 132(A), it may be the type ofmicro-coating layer that provides higher adhesive property than thefirst type of micro-coating layer 132(A). This way, the second type ofmicro-coating layer 132(B) provided at the edges or on the surfaces ofthe encapsulation 104 and the printed circuit 134 can improve thesealing at the respective regions to suppress possible corrosion of theconductive lines thereunder.

In the embodiments where the second region is provided in between thefirst region and the encapsulation, the second type of micro-coatinglayer may be overflowed on at least some part of the encapsulation 104.Similarly, in the embodiments where the second region is provided inbetween the first region and the printed circuit 134, the second type ofmicro-coating layer is overflowed on at least some part of the printedcircuit 134. As described above with reference to FIGS. 17A-17C, coatingat least some upper surface of the encapsulation 104 and/or the printedcircuit 134 at their edges can further improve the sealing at therespective regions. In some embodiments, the first type of micro-coatinglayer 132(A) provided in the bend allowance section may be coated overthe second type of micro-coating layer 132(B) and over at least someupper surface of the encapsulation 104 and/or the printed circuit 134 attheir edges.

In some embodiments, the first type of micro-coating layer coated in thefirst region may be coated on the second type of micro-coating layer.Further, the first type of micro-coating layer in the first region maybe coated on at least some part of the encapsulation and/or at leastsome part of the printed circuit.

In addition to having higher adhesion property than the first type ofmicro-coating layer 132(A), the second type of micro-coating layer mayinclude one or more of getter materials dispersed therein. The gettermaterials absorb and/or react with the water vapor, which can corrodethe wire traces under the micro-coating layer 132. In some embodiments,a third type of micro-coating layer 132(C) including one or more gettermaterials may be provided underneath the first type of micro-coatinglayer 132(A) and the second type of micro-coating layer 132(B) asdepicted in FIG. 20B.

For convenience, the bend allowance section provided with the multiplekinds of micro-coating layers is between a display area with theencapsulation and a non-display area with the printed circuit 134.However, it should be noted that the bend allowance section providedwith the multiple kinds of micro-coating layers can be provided betweentwo portions of the flexible display apparatus 100, each including adisplay area therein. Also, the bend allowance section provided with themultiple kinds of micro-coating layers can be provided between twonon-display areas, which may be attached with a printed circuit.

Divided VSS-VDD Wire Trace

Spreading dynamic of the micro-coating layer 132 over the wire tracescan be affected by the trace design of the wire traces. Morespecifically, patterning of the insulation layers along the wire tracein the bend portion of the flexible display 100 creates recessed areasand protruded areas, which essentially become a micro-grooved surface tobe covered by the micro-coating layer 132.

When applying the strain-reducing trace design in the wire traces,patterning of the insulation layers around the split sub-traces createsthe recessed open area, which is surrounded by the protruded stack ofwire traces. During coating of the micro-coating layer 132, some portionof the micro-coating layer droplet can permeate into the recessed openarea. It can hinder the spreading and reduce the maximum spreadingdiameter of the micro-coating layer 132 on such a micro-grooved surface,and result in some part of the bend portion being exposed without themicro-coating layer 132.

Decrease in the wettability of micro-coating layer 132 by thedistribution of the recessed areas and the protruded areas may bemagnified even more in the area over the wire trace applied with thegrid-like trace design shown in FIG. 11B. To counteract the viscid drag,in some embodiments, a wire trace, which includes multiple diamond-chaintraces adjoined side-by-side, can be provided with a rail between twoparts of the wire trace.

Referring to FIG. 21, a wire trace with a grid-like tracestrain-reducing trace design is provided with an elongated channelbetween divided grid-parts of the wire trace. Within the elongatedchannel, the conductive line 120 is not formed. Also, at least some ofthe inorganic insulation layers on the base layer 106 are removed in theelongated channel. The elongated channel between the grid-parts of thewire trace extends from the signal supplying side to the signalreceiving side of the wire trace. That is, the elongated channel may beextended in the direction parallel to the bending direction. It shouldbe noted that the separated parts of the wire trace on one side of theelongated channel is connected to the part of the wire trace on theopposite side of the elongated channel, and thus both parts of the wiretrace transmit the identical signal. The connection between the dividedparts of the wire trace may be achieved at one or both ends of the wiretrace by a conductive path, which may be a part of the wire trace. Theconnection of the divided parts of the wire trace may be achieved withinthe bend allowance section or outside the bend allowance section.

Even though the parts of the wire trace on each side of the elongatedchannel has the grid-like trace design, the reduced number ofdiamond-chain traces adjoined in each grid-part and the channel betweenthe grid-parts can reduce the viscid drag of the micro-coating layer132. More importantly, the elongated recessed channel between the partsof the wire trace serves as a path that improves the wettability of themicro-coating layer 132 over the wire trace. In sum, increase in themaximum spread diameter of the micro-coating layer 132 can be achievedby positioning one or more elongated channel within the wire having thegrid-like strain-reducing trace design.

It should be noted that the resistance of the wire trace can increasewith the elongated channel dividing the wire trace into multiplegrid-parts. Increase in the resistance of the wire can raise thetemperature of the wire trace when it is supplied with a signal.Accordingly, the number of elongated channels provided in a single wiretrace can depend on the signal transmitted via the wire trace. In somecases, the size of each diamond shaped link in a grid-like wire tracemay be larger than the size of diamond-shaped links in other wire tracesof the flexible display 100.

In one suitable configuration, one or more of power signal wires of theflexible display 100, such as the VDD and/or the VSS, has the grid-likewire trace formed of multiple diamond-chain traces adjoined side-by-sideas depicted in FIG. 21. The power signal wire trace includes one or moreelongated channels in its grid-like wire trace. Each of the elongatedchannels is provided between two divided grid parts, which are on theopposite sides of the elongated channel. The divided grid parts areconnected at one or both ends of the power signal wire. The size of thedivided grid parts may be substantially the same. That is, the number ofdiamond-chain traces forming a gird part on one side of the elongatedchannel may be the same as the number of diamond-chain traces forming agird part on the opposite side. If desired, however, the number ofdiamond-chain traces adjoined to each other to form one grid part maydiffer from the number of diamond-chain forming another grid part.

Corrosion Resistant Printed Circuit Film

As mentioned, one or more driving circuits, such as a display drive-ICand/or a touch drive-IC, can be disposed on the printed circuit.Conductive lines on the printed circuit transmits signals from and tothe components provided on the base layer 106 as well as the componentsdisposed on another printed circuit. Referring to FIG. 22, on one end ofthe first printed circuit 134, the conductive lines are arranged to bein contact with the conductive lines on the base layer 106. On the otherend of the first printed circuit 134, the conductive lines are routed tobe in contact with another printed circuit 136 (e.g., PCB), which mayinclude additional circuits and/or components provided thereon. In thisexample, the first printed circuit 134 attached to the base layer 106 isdescribed as a chip-on-film (COF), and the second printed circuit 136attached to the first printed circuit 134 is described as a printedcircuit board (PCB). The area where the part of the first printedcircuit 134 and the base layer 106 are attached together may be referredto as the “Flex-on-Panel (FOP) area.” Also, the area where the printedcircuits are attached together may be referred to as the “flex-on-flex(FOF) area.” It should be noted that the second printed circuit 136 maynot be needed in some embodiments of the flexible display 100. Forinstance, components on the first printed circuit 134 and the secondprinted circuit 136 may be provided on a single printed circuit, whichis attached to the base layer 106.

In the FOP area or the FOF area of the first printed circuit 134, partof the conductive lines can serve as a connector (e.g., pads or pins),which is to be connected to the corresponding connector on the baselayer 106 and the connector of the second printed circuit 136. In thecontact areas, an anisotropic conductive adhesive (e.g., anisotropicconductive film: ACF) or other types of adhesives may be providedbetween the connectors. Before bonding the first printed circuit 134 tothe base layer 106 and the second printed circuit 136, tests are usuallyperformed to inspect whether the conductive lines on the first printedcircuit 134 are properly connected to the components disposed thereon.However, the conductive lines are disposed in a very narrow pitch inFOP/FOF areas, and thus it is difficult to supply/receive test signalson the conductive lines at those areas. Therefore, the conductive lineson the first printed circuit are routed beyond the FOP/FOF areas to anarea where they are arranged with a larger pitch and/or provided withtest pads.

Similar to the test pads 120_P and the test lines 120_C described inreference to FIGS. 8A-8B, the part of the conductive lines on the firstprinted circuit 134 routed beyond the FOP/FOF areas can be removed fromthe first printed circuit 134 when scribing/chamfering the first printedcircuit 134 into a desired shape and size. Thus, the conductive linesremaining on the first printed circuit 134 can be extended until thescribed/chamfered edges of the first printed circuit 134. For reliableconnection between the connectors, scribing of the first printed circuit134 is usually performed with a certain margin between the scribed edgeand the contact area where the part of the conductive lines serve as theconnectors.

As mentioned, the part of the conductive lines routed outside thecontact area toward the scribed edge, which is sometimes referred to asthe “valley pattern”, is especially susceptible to corrosion from themoisture and gasses passing through the micro-coating layer 132.Accordingly, embodiments of the flexible display 100 may employ severalfeatures that can help minimize corrosion of the conductive lines on thefirst printed circuit 134. FIG. 23A is a plan view illustrating anexemplary configuration of the conductive lines in the FOP area on thefirst printed circuit 134. As shown, certain conductive lines disposedon the first printed circuit 134 are arranged not to extend beyond thecontact areas. That is, on the first printed circuit 134, someconnectors are provided with valley patterns while some of the selectedconnectors are provided without the valley patterns. The conductivelines that end at the contact area without the valley pattern may be theones that are routed between the FOP area and the FOF area without beingconnected to the components on the first printed circuit 134, such asthe Drive-IC 138. Such conductive lines are routed on the first printedcircuit 134 simply to provide interconnections between the components onthe base layer 106 and the components on the second printed circuit 134,and thus, chances of defects in such conductive lines are very slim.Without the valley pattern, the end of the conductive line is not cut bythe scribing process, and the outer layer (e.g., Sn layer) of theconductive line can cover the inner layer (e.g., Cu layer) of theconductive line, which in turn suppresses corrosion. Also, eliminatingthe valley pattern of such bypassing conductive lines can increase thedistance X between the valley patterns of other conductive lines.Electrical flow between anodic metal and cathode metal being one of theessential element for corrosion, increase in the distance between thevalley patterns can help reduce corrosion on those valley patterns. Inaddition, increasing the distance X between the valley patterns canlower the chances of short between the conductive lines caused by thecorrosion debris and other deposits.

For the similar reason described above, in some embodiments, a dummyconnector may be provided between the connectors that transmit signalsof a voltage large difference from each other. Referring to FIG. 23B, adummy connector can be positioned between a conductive line fortransmitting VGH and a conductive line for transmitting VGL. Also, adummy connector can be positioned between the VSS line connector and theVDD line connector. The VGH/VGL and VDD/VSS line connectors have thevalley pattern extending to the scribed edge of the first printedcircuit 134, whereas the dummy connectors do not have the valleypatterns. The space between the connectors of the oppositely chargedconductive lines is increased by the width of the dummy connector. Theend of the dummy connector is spaced apart from the scribed edge of thefirst printed circuit 134. As such, corrosion control on the valleypatterns of the conductive lines with large voltage difference can berealized.

In some cases, some of the signals, for instance the gate high/lowsignals and/or the power signals, may be transmitted by using a group ofseveral conductive lines positioned next to each other on the firstprinted circuit 134. Also, conductive lines transmitting similar signals(e.g., clock signals) may be arranged next to each other on the firstprinted circuit 134. In such cases, inspection on all of the conductivelines of the same group may not be necessary. Accordingly, in someembodiments, at least one or more of connectors in a group of adjacentlypositioned connectors transmitting the same or similar type of signalsmay be provided on the first printed circuit 134 without the valleypattern.

Referring to FIG. 23C, connectors for transmitting similar type ofsignals are provided adjacent to each other, which are denoted as“Connector Group.” Also, adjacently positioned connectors fortransmitting the same signal are denoted as “Multi-Pin Connector.” Asshown, at least one of the connectors among the multi-pin connector maybe formed on the first printed circuit 134 without the valley pattern.Similarly, at least one of the connectors among the group of connectorsthat provides similar signals may not be provided with the valleypattern. For instance, any one of the conductive lines CLK1, CLK2 andCLK 3 may end with a connector without the valley pattern. This way,distance X between the remaining valley patterns can be increased, whichcan help reduce corrosion on those valley patterns. Further, chances ofshort between the valley patterns by the corrosion debris and otherdeposits can be reduced by increasing the distance X between the valleypatterns.

In some embodiments, the connector without the valley pattern may be thefirst and/or the last connector among the group of connectors. In FIG.23C, the connector B, which is positioned next to the connector group orthe multi-pin connectors, may be configured to transmit a different typeof signal from the signals transmitted on the connector group and themulti-pin connectors. By way of example, the connectors in the connectorgroup may be configured to transmit clock signals and the connector Bmay be configured to transmit any one of the VGH, VGL, VDD and VSSsignals. Among the connectors included in connector group and themulti-pin connectors, one that is positioned immediately adjacent to theconnector B may be provided on the first printed circuit 134 without thevalley pattern.

Furthermore, in some embodiments, solder resist (SR) covering theconductive lines outside the contact area may also be provided over thevalley patterns along the scribed edge as depicted in FIG. 23D. In thisregard, the solder resist (SR) may be coated over the valley patternsprior to scribing the first printed circuit 134. Alternatively, thesolder resist (SR) may be coated over the valley patterns after thescribing of the first printed circuit 134 is performed. In the lattercase, the solder resist (SR) may cover the exposed cross-sectional sidesurface of the valley pattern. While the configurations of connectorsare described in reference to the connectors in FOP area, suchconfigurations can also be used for the connectors in the FOF area.

Although the concepts and teachings in the present disclosure aredescribed above with reference to OLED display technology, it should beunderstood that several features may be extensible to any form offlexible display technology, such as electrophoretic, liquid crystal,electrochromic, displays comprising discreet inorganic LED emitters onflexible substrates, electrofluidic, and electrokinetic displays, aswell as any other suitable form of display technology.

As described above, a flexible display 100 may include a plurality ofinnovations configured to allow bending of a portion or portions toreduce apparent border size and/or utilize the side surface of anassembled flexible display 100. In some embodiments, bending may beperformed only in the bend portion and/or the bend allowance sectionhaving only the conductive line 120 rather than active displaycomponents or peripheral circuits. In some embodiments, the base layer106 and/or other layers and substrates to be bent may be heated topromote bending without breakage, then cooled after the bending. In someembodiments, metals such as stainless steel with a passive dielectriclayer may be used as the base layer 106 rather than the polymermaterials discussed above. Optical markers may be used in severalidentification and aligning process steps to ensure appropriate bendsabsent breakage of sensitive components. Components of the flexibledisplay 100 may be actively monitored during device assembly and bendingoperations to monitor damage to components and interconnections.

Constituent materials of conductive line 120 and/or insulation layersmay be optimized to promote stretching and/or compressing rather thanbreaking within a bending area. Thickness of a conductive line 120 maybe varied across a bending area and/or the bend allowance section tominimize stresses about the bend portion or the bend allowance sectionof the flexible display 100. Trace design of conductive line 120 andinsulation layers may be angled away from the bending direction (i.e.,tangent vector of the curvature), meandering, waving, or otherwisearranged to reduce possibility of severance during bending. Thethickness of the conductive line 120, insulation layers and othercomponents may be altered or optimized in the bend portion of theflexible display 100 to reduce breakage during bending. Bend stressesmay be reduced by adding protective micro-coating layer(s) overcomponents in addition to disclosed encapsulation layers. Conductivefilms may be applied to the conductive line 120 before, during, or afterbending in a repair process. Furthermore, the constituent materialand/or the structure for conductive line 120 in a substantially flatarea of a flexible display 100 may differ from the conductive line 120in a bend portion and/or the bend allowance section.

These various aspects, embodiments, implementations or features of thedescribed embodiments can be used separately or in any combination. Theforegoing is merely illustrative of the principles of this invention andvarious modifications can be made by those skilled in the art withoutdeparting from the scope of the invention.

What is claimed is:
 1. A display device comprising: a flexible base layer provided in a rounded shape; an array of organic light-emitting diode (OLED) elements, provided in the rounded shape on the flexible base layer; and an upper layer on the array of OLED element, the upper layer having a shape corresponding to the shape of the flexible base layer, wherein the upper layer on the array of OLED element provides clearance of a chamfer line of the flexible base layer to reduce damage in one or more insulation layers interposed between the upper layer and the flexible base layer. 